Cell culture methods and devices utilizing gas permeable materials

ABSTRACT

Gas permeable devices and methods are disclosed for cell culture, including cell culture devices and methods that contain medium at heights, and certain gas permeable surface area to medium volume ratios. These devices and methods allow improvements in cell culture efficiency and scale up efficiency.

RELATED APPLICATION

The present application claims priority to U.S. application Ser. No.10/961,814 filed Oct. 8, 2004 which claims priority to U.S. ProvisionalApplication No. 60/509,651 filed Oct. 8, 2003, which is herebyincorporated herein in its entirety by reference.

1. TECHNICAL FIELD

The technical field of the invention relates to methods and devices thatimprove cell culture efficiency. They utilize gas permeable materialsfor gas exchange, allow an increased height of cell culture medium,reduce the ratio of gas permeable device surface area to medium volumecapacity, and integrate traditional cell support scaffolds. A variety ofbenefits accrue, including more efficient use of inventory space,incubator space, disposal space, and labor, as well as reducedcontamination risk.

2. DISCUSSION OF LIMITATIONS OF CONVENTIONAL TECHNOLOGIES DESCRIBED INRELATED ART

The culture of cells is a critical element of biotechnology. Cells arecultured in small quantities during the research stage, and typicallythe magnitude of the culture increases as the research moves towards itsobjective of benefiting human and animal health care. This increase inmagnitude is often referred to as scale up. Certain devices and methodshave become well established for research stage cell culture becausethey allow a wide variety of cell types to be cultured, and aretherefore useful to the widest audience. These devices include multiplewell tissue culture plates, tissue culture flasks, roller bottles, andcell culture bags. Unfortunately, these devices are inefficient and theybecome even less efficient in terms of labor, contamination risk, andcost during scale up. There is a need to create alternative devices andmethods that research and retain scale up improve research and scale upefficiency. This discussion identifies many of the limitations inconventional technologies and points towards solutions that aresubsequently described in more detail.

One attribute that is essential for research scale cell culture is a lowlevel of complexity. Devices that minimize complexity do not requireancillary equipment to mix or perfuse the cell culture medium. They areoften referred to as static devices. Static devices can be subdividedinto two broad categories, 1) those that are not gas permeable andoxygenate the cells by way of a gas/liquid interface and 2) those thatare gas permeable and oxygenate the cells by way of gas transfer throughthe device housing. The traditional petri dish, multiple well tissueculture plate, tissue culture flask, and multiple shelf tissue cultureflask are in the first category. The cell culture bag andcompartmentalized flasks are in the second category. All of these staticdevices are inefficient for a variety of reasons, including the limitedheight at which medium can reside in them.

Medium height is limited in the petri dish, multiple well tissue cultureplate, tissue culture flask, and multiple shelf tissue culture flask dueto the method of providing gas exchange. To meet cellular demand, oxygenmust diffuse from a gas/liquid interface to the lower surface of thedevice where cells reside. To ensure adequate oxygen supply, the maximumheight of cell culture medium recommended for use in these devices isabout 3 mm.

Limited culture medium height leads to disadvantages. It creates a smallmedium volume, which can only support a small quantity of cells. Mediumneeds to be continually removed and added to sustain cultures, whichincreases handling frequency, labor, and contamination risk. The onlyway to culture more cells in a device is to make the footprint of thedevice larger so that more medium can be present. Creating a device withlarge footprint is challenging from a manufacturing standpoint, quicklyoutgrows the limited amount of space available in a typical incubatorand flow hood, and makes the device more difficult to handle. Thus,commercially available cell culture devices are small. Scaling up theculture therefore requires using multiple devices or selecting moresophisticated, complex, and costly alternatives.

The tissue culture flask provides a good example of the problemsinherent to static devices that rely upon a gas/liquid interface tofunction. Tissue culture flasks allow cells to reside upon surfacestypically ranging from 25 cm² to 225 cm² in area. The height of mediumthat is recommended for tissue culture flasks is between 2 mm and 3 mm.For example, Corning® recommends a 45 ml-67.5 ml working volume for itsT-225 cm² flask. Thus, a 1000 ml culture requires between 15 and 22T-225 cm² flasks. Not only does this require 15 to 22 devices to be fed,leading to increasing labor and contamination risk, it also makes veryinefficient use of space because flasks are designed in a manner thatholds about 95% gas and only 5% medium. For example, the body of atypical T-175 flask has a footprint approximately 23 cm long by 11 cmwide, is about 3.7 cm tall, and therefore occupies about 936 cm³ ofspace. However, it typically operates with no more than about 50 ml ofmedium. Thus, the medium present in the body (50 ml), relative to thespace occupied by the body (936 cm³) demonstrates that nearly 95% of theflask's content is merely gas. This inefficient use of space addsshipping, sterilization, storage, and disposal cost, in addition towasting precious incubator space.

Another commonly used research scale cell culture device is the multiplewell tissue culture plate. As with the traditional tissue culture flask,maintaining a gas/liquid interface at a height of only 2 mm to 3 mmabove the bottom of each well is standard operating procedure. In orderto provide protection against spillage when the plates are moved aroundthe cell culture laboratory, each well of a typical commerciallyavailable 96 well tissue culture plate is about 9 mm deep. The depthincreases up to about 18 mm for a six well tissue culture plate. In thecase of the ninety-six well plate, gas occupies about 75% of each welland medium occupies about 25% of each well. In the case of the six-wellplate, gas occupies about 95% of each well and medium occupies about 5%of each well. This inefficient geometry adds cost to device shipping,sterilization, storage, and disposal.

In many applications, the need to frequently feed the culture byremoving and replacing the small volume of medium can be problematic.For example, if the purpose of the multiple well tissue culture plate isto perform experiments, manipulating the medium could affect the outcomeof those experiments. Also, because the medium volume is so small, adetrimental shift in solute concentration can occur with just a smallamount of evaporation. A multiple well tissue culture plate that allowedmedium to reside at an increased height without loss of cell culturefunction would be superior to the traditional plate by minimizing themanipulations needed to keep the culture alive, and reducing themagnitude of concentration shifts caused by evaporation.

Frequently medium exchange is also time consuming, costly, and leads toelevated contamination risk. Attempts to mitigate the problem by specialliquid handling equipment such as multi-channel pipettes do not addressthe source of the problem, low medium height. The best solution is toallow more medium to reside in each well. Unfortunately, that solutionis not possible with traditional plates due to the need for gas exchangeby way of the gas/liquid interface.

Better alternatives to traditional devices are needed. If tissue culturedevices were available that did not rely solely upon a gas/liquidinterface to function, were just as easy to use as traditional flasksand multiple well plates, allowed more cells to be cultured in a deviceof the same footprint, and were easily and linearly scalable, theefficient gains would translate into reduced costs for those using cellsto advance human and animal health care. It will be shown herein how theuse of gas permeable materials and novel configurations can achieve thisobjective.

Cell culture devices that eliminate the gas/liquid interface as the solesource of gas exchange have been proposed, and made their way into themarket. This approach relies on the use of a lower gas permeablemembrane to bring gas exchange to the bottom of the medium. That, asopposed to sole reliance on gas/liquid interfaces, allows more gastransfer. The proposed and commercially available devices include cellculture bags, compartmentalized gas permeable flasks, gas permeablecartridges, gas permeable petri dishes, gas permeable multiple wellplates, and gas permeable roller bottles.

Unfortunately, each of the gas permeable devices has inherentinefficiencies and scale up deficiencies. Primary limitations of cellculture bags, gas permeable cartridges, gas permeable petri dishes, gaspermeable multiple well plates, compartmentalized gas permeable flasks,and gas permeable roller bottles include limited medium height,excessive gas permeable surface area to medium volume ratios, and poorgeometry for culturing adherent cells. This has the effect of forcingnumerous devices to be required for scale up, restricting device designoptions, and increasing cost and complexity as scale up occurs.

Close examination of prior art surrounding gas permeable devicesdemonstrates how conventional wisdom, and device design, limits theheight of medium and the volume of medium that resides in them. In the1976 paper entitled Diffusion in Tissue Cultures on Gas-permeable andImpermeable Supports (Jensen et al., J. Theor. Biol. 56, 443-458(1976)), the theory of operation for a closed container made of gaspermeable membrane is analyzed. Jensen et al. describes diffusion as themode of solute transport in the medium and the paper states that“diffusion proceeds according to Fick's laws.” Jensen et al. state “FIG.2 [of Jensen et al.] shows the diffusional characteristics for cellscultured in a bag made of gas permeable material.” FIG. 1A, herein,shows FIG. 2 of Jensen et al. in which D_(c)m is the diffusion constantof medium. FIG. 1B, herein, shows FIG. 3 of Jensen et al. in which themodel of steady state values for PO ₂ and PCO ₂ in a gas permeablecontainer are shown as a linear decay throughout the medium, based ondiffusion.

In 1977, Jensen (Jensen, Mona D. “Mass cell culture in a controlledenvironment”, Cell Culture and its Applications, Academic Press 1977)described a “major innovation” by the use of “gas permeable, nonporousplastic film” to form a cell culture device. FIG. 2, herein, shows FIG.2 of Jensen. As shown in FIG. 2, herein, the device created a very lowheight of medium, only 0.76 mm, and a very high gas permeable surface tomedium volume ratio. For scale up, the device gets as long as 30 feetand is perfused using custom equipment.

In 1981, Jensen (Biotechnology and Bioengineering. Vol. XXIII, Pp.2703-2716 (1981)) specifically stated “culture vessel design mustincorporate a small diffusional distance which is fixed and constant forall the cells cultured. The design must be such that scaling-up theculture does not change the diffusion distance.” Indeed, theconventional wisdom that medium should not reside at a height very farfrom the gas permeable membrane continues to this day, as evidenced bythe commercial products that utilize gas permeable materials and thepatents that are related to them. Furthermore, a high gas permeablesurface to medium volume ratio continues.

A variety of gas permeable cell culture devices have entered the marketand been proposed since 1981. However, continued reliance on diffusionas a primary design factor appears to be the case based upon review ofthe patents, device design, device specifications, and operatinginstructions for gas permeable devices. As design criteria, the modelfor diffusion limits medium height, leads to high gas permeable surfaceto medium volume ratios, and contributes to inefficient device geometry.

Commercially available gas permeable cell culture devices in the form ofbags are currently a standard device format used for cell culture. Aswith the configuration of Jensen, these products allow gas exchangethrough the lower and upper surface of the medium via gas permeablematerials. Unlike the device presented by Jensen, perfusion is notrequired. Typically they are not perfused, and reside in a cell cultureincubator. This reduces cost and complexity and has made them anaccepted device in the market. However, the limited distance between thegas permeable membranes when cell culture medium resides in them has theeffect of making them geometrically unsuitable for efficient scale up.As more medium is needed, bag size must increase proportionally in thehorizontal direction. Thus, they are generally unavailable in sizesbeyond 2 liters, making numerous devices required for scale up.Furthermore, they are not compatible with the standard liquid handlingtools used for traditional devices, adding a level of complexity forthose performing research scale culture.

Bags are fabricated by laminating two sheets of gas permeable filmstogether. A typical bag cross-section is shown in FIG. 3 taken from U.S.Pat. No. 5,686,304, which has been commercialized at the Si-Culture™ bag(Medtronic Inc.). A beneficial feature of traditional static cellculture devices is a uniform distribution of medium over the area wherecells reside. Those skilled in the art specifically take great care tolevel incubators for the purpose of ensuring that the medium resides ata constant height throughout the device. By looking at the bagcross-section of FIG. 3, it can be seen how medium does not reside at auniform height above the entire lower gas permeable film, no matter howlevel the incubator is. Since the films mate at the perimeter, medium isforced to reside at a different height near the perimeter than elsewherein the bag. As medium volume increases, the bag begins to take acylindrical shape and medium distribution becomes worse. Cells can besubjected to potential nutrient gradients due to the non-uniform shape.If too much medium is in the bag, the lower surface will reside in anon-horizontal state. That also creates problems. Suspension cellsresiding in the bag will not distribute uniformly. Instead, they willgravitationally settle in the low point, pile up, and die as nutrientand oxygen gradients form within the pile. In the case of adherentcells, they will not seed uniformly because the amount of inoculumresiding in each portion of the bag will vary. In addition to thegeometric problems created if bags are overfilled, the weight of mediumin excess of 1000 ml can also damage the bag as described in U.S. Pat.No. 5,686,304. Even if the geometric limitations of bags were overcome,instructions and patents related to the bags and other gas permeabledevices indicate a limit exists based on the belief that diffusionbarriers prevent devices from functioning when medium resides at toogreat a height.

Cell culture bags are commercially available from OriGen BiomedicalGroup (OriGen PermaLife™ Bags), Baxter (Lifecell® X-Fold™ related toU.S. Pat. Nos. 4,829,002, 4,937,194, 5,935,847, 6,297,046 B1), Medtronic(Si-Culture™, U.S. Pat. No. 5,686,304), Biovectra (VectraCell™), andAmerican Fluoroseal (VueLife™ Culture Bag System, covered by U.S. Pat.Nos. 4,847,462 and 4,945,203). The specifications, operatinginstructions, and/or patents dictate the medium height and the gaspermeable surface area to medium volume ratio for each product.

Pattillo et al. (U.S. Pat. Nos. 4,829,002 and 4,937,194 assigned toBaxter International Inc.) states that typically bags are “filled toabout one quarter to one half of the full capacity, to provide arelatively high ratio of internal surface area of volume of the mediaand cells, so that abundant oxygen can diffuse into the bag, and carbondioxide can diffuse out of the bag, to facilitate cell metabolism andgrowth.” In light of Pattillo et al. the best medium height attained forthe Baxter Lifecell® X-Fold™ bags is for their 600 cm² bag, which yieldsa medium height of 1.0 cm to 2.0 cm and a gas permeable surface area tomedium volume ratio of 2.0 cm²/ml to 1.0 cm²/ml.

The product literature for the VectraCell™ bag states “VectraCell 1 Lcontainers can hold up to 500 mL of media. VectraCell 3 L containers canhold up to 1500 mL of media.” Thus, as with the Baxter bags, maximummedium capacity is at one half the bags total capacity. Of the variousbag sizes offered, the 3 L bag allows the highest medium height, 1.92cm, and has the lowest gas permeable surface area to medium volume ratioof 1.04 cm²/ml.

A 1.6 cm medium height is recommended for the Si-Culture™ bag in theproduct literature and specified in U.S. Pat. No. 5,686,304 when itresides on an orbital shaker that physically mixes the medium. Thatleads to a gas permeable surface area to medium volume ratio of 1.25cm²/ml when used in a mixed environment. Since mixing is generally usedto break up diffusional gradients and enhance solute transfer, oneskilled in the art would conclude that medium height should be reducedwhen this bag is not placed on an orbital shaker.

The product literature for the VueLife™ bag specifically recommendsfilling VueLife™ Culture Bags with media at a height of no more than onecentimeter thick, because “additional media might interfere withnutrient or gas diffusion.” Thus, diffusional concerns limit mediumheight in the VueLife™ bags. That leads to a gas permeable surface areato medium volume ratio of 2.0 cm²/ml at a medium height of 1.0 cm.

The product literature for the OriGen PermaLife™ bags specify nominalvolume at a medium height of 1.0 cm, the equivalent height of theVueLife™ bags. Of the various PermaLife™ bags offered, their 120 ml bagoffers the lowest gas permeable surface area to medium volume ratio of1.8 cm²/ml.

The net result of the limited medium height is that culture scale upusing these products is impractical. For example, if the LifecellX-Fold™ bag were scaled up so that is could contain 10 L of medium at amedium height of 2.0 cm, its footprint would need to be at least 5000cm². Not only is this an unwieldy shape, the footprint can quicklyoutsize a standard cell culture incubator, leading to the need forcustom incubators. Also, the gas transfer area utilized in the bags islarger than necessary because all of these configurations rely upon boththe upper and lower surfaces of the bag for gas transfer.

This impractical geometry has restricted the size of commerciallyavailable bags. Recommended medium volume for the largest bag from eachsupplier is 220 ml for the OriGen PermaLife™ bags, 730 ml for theVueLife™ bags, 1000 ml for the Lifecell® X-Fold™ bags, 1500 ml for theVectraCell™ bags, and 2000 ml for the Si-Culture™ bags when shaken.Therefore, scale up requires the use of numerous individual bags, makingthe process inefficient for a variety of reasons that include increasedlabor and contamination risk.

Another deficiency with cell culture bags is that they are not as easyto use as traditional flasks. Transport of liquid into and out of themis cumbersome. They are configured with tubing connections adapted tomate with syringes, needles, or pump tubing. This is suitable for closedsystem operation, but for research scale culture, the use of pipettes isan easier and more common method of liquid handling. The inability touse pipettes is very inconvenient when the desired amount of medium tobe added or removed from the bags exceeds the 60 ml volume of a typicallarge syringe. In that case the syringe must be connected and removedfrom the tubing for each 60 ml transfer. For example, a bag containing600 ml would require up to 10 connections and 10 disconnections with a60 ml syringe, increasing the time to handle the bag and the probabilityof contamination. To minimize the number of connections, a pump can beused to transfer medium. However, this adds cost and complexity tosmall-scale cultures. Many hybridoma core laboratories that utilize cellculture bags fill them once upon setup, and do not feed the cells againdue to the high risk of contamination caused by these connections andthe complexity of pumps.

Matusmiya et al. (U.S. Pat. No. 5,225,346) attempts to correct theproblem of liquid transport by integrating the bag with a medium storageroom. The culture room and medium storage room are connected and whenfresh medium is needed, medium is passed from the medium room to theculture room. While this may help in medium transport, there is noresolution to the limited medium height and high gas permeable surfacearea to medium volume ratios that limit bag scale up efficiency. Thedisclosure presents a medium height of 0.37 cm and gas permeable surfacearea to medium volume ratio of 5.4 cm²/ml.

Cartridge style gas permeable cell culture devices have been introducedto the market that, unlike cell culture bags, have sidewalls. Thesetypes of devices use the sidewall to separate upper and lower gaspermeable films. That allows uniform medium height throughout thedevice. Unfortunately, these devices are even less suitable for scale upthan bags because they only contain a small volume of medium. The smallmedium volume is a result of an attempt to create a high gas permeablesurface area to medium volume ratio.

One such product called Opticell® is provided by BioChrystal Ltd. Thisproduct is a container, bounded on the upper and lower surfaces by a gaspermeable silicone film, each with a surface area of 50 cm². Thesidewall is comprised of materials not selected for gas transfer, butfor providing the rigidity needed to separate the upper and lower gasmembranes. Product literature promotes its key feature, “two growthsurfaces with a large surface area to volume ratio.” In an article forGenetic Engineering News (Vol. 20 No. 21 Dec. 2000) about this product,patent applicant Barbera-Guillem states “with the footprint of amicrotiter plate, the membrane areas have been maximized and the volumeminimized, resulting in a space that provides for large growth surfaceswith maximum gas interchange.” The operating protocol defining how touse this product specifies introduction of only 10 ml of medium, therebylimiting the height at which medium can reside to 0.2 cm. U.S. patentapplication Ser. No. 10/183,132 (filed Jun. 25, 2002), associated withthis device, states a height up to 0.5 inches (1.27 cm) is possible, butmore preferred would be a height of about 0.07 to about 0.08 inches(0.18 cm to about 0.2 cm). WO 00/56870, also associated with thisdevice, states a height up to 20 mm is possible, but more preferredwould be a height of 4 mm. Even if the greater height of 1.27 cmdescribed in the patent were integrated into the commercial device, thatmedium height does not exceed that allowed in bags. Furthermore, thatwould only reduce the gas permeable surface area to medium volume ratioto 1.00 cm²/ml, which is similar to the bag. U.S. patent applicationSer. No. 10/183,132 shows a configuration in which only one side of thedevice is gas permeable. In that configuration, which was notcommercialized, a gas permeable surface area to medium volume ratio of0.79 cm²/ml at a medium height of 0.5 inches (1.27 cm) would beattained, which is somewhat lower than that of cell culture bags.Therefore, despite a sidewall, even when the geometry allows the maximummedium height, there is not improved scale up efficiency relative tobags.

Cartridge style gas permeable cell culture devices have also beenintroduced to the market by Laboratories MABIO-International®, calledCLINIcell® Culture Cassettes. Like the Opticell®, neither the productdesign nor the operating instructions provide for an increase in mediumheight, or a reduced gas permeable surface area to medium volume ratio,relative to bags. The operating instructions for the CLINIcell® 25Culture Cassette state that no more than 10 ml of medium should resideabove the lower 25 cm² gas permeable surface. Since the surface area ofthe lower gas permeable material is only 25 cm², that creates a mediumheight of only 0.4 cm. Also, since the top and bottom of the device arecomprised of gas permeable material, there is a high gas permeablesurface area to medium volume ratio of 5.0 cm²/ml. The operatinginstructions for the CLINIcell® 250 Culture Cassette state that no morethan 160 ml of medium should reside above the lower 250 cm² gaspermeable surface, leading to a low medium height of 0.64 cm and a highgas permeable surface area to medium volume ratio of 3.125 cm²/ml.

Cartridge style gas permeable cell culture devices have recently beenintroduced to the market by Celartis, called Petaka™. Like the Opticell®and CLINIcell® Culture Cassettes, these devices also have a sidewallthat functions as a means of separating the upper and lower gaspermeable films. Unlike those products, it is compatible with a standardpipettes and syringes, so it improves convenience of liquid handling.Yet, neither the product design nor the operating instructions providefor an increase in medium height, or a reduced gas permeable surfacearea to medium volume ratio, relative to bags. The operatinginstructions state that no more than 25 ml of medium should residebetween the upper and lower gas permeable surfaces, which comprise atotal surface area of 160 cm². Product literature specifies “optimizedmedia/surface area” of 0.156 ml/cm². Thus, the medium height is only0.31 cm and the optimized gas permeable surface area to medium volumeratio is 6.4 cm²/ml.

The limitations of the commercially available cartridge style gaspermeable devices for scale up become clear when reviewing the maximumculture volume available for these devices. Opticell® provides up to 10ml of culture volume, CLINIcell® Culture Cassettes provide up to 160 mlof culture volume, and Petaka™ provides up to 25 ml of culture volume.Therefore, just to perform a 1000 ml culture, it would take 100Opticell® cartridges, 7 CLINIcell® Culture Cassettes, or 40 Petaka™cartridges.

Vivascience Sartorius Group has introduced gas permeable petri dishesinto the market called petriPERM. The petriPERM 35 and petriPERM 50 areproducts in the form of traditional 35 mm and 50 mm diameter petridishes respectively. The bottoms are gas permeable. The walls of thepetriPERM 35 mm dish and petriPERM 50 mm dish are 6 mm and 12 mm highrespectively. Vivascience product specifications show the petriPERM 35has a gas permeable membrane area of 9.6 cm² and a maximum liquid volumeof 3.5 ml, resulting in a maximum medium height of 0.36 cm., and thepetriPERM 50 has a gas permeable membrane area of 19.6 cm² and a maximumliquid volume of 10 ml, resulting in a maximum medium height of 0.51 cm.The petriPERM products are designed with a cover that allows the uppersurface of medium to be in communication with ambient gas, and a lowergas permeable material that allows the lower surface of the medium to bein communication with ambient gas. Thus, the minimum gas permeablesurface area to medium volume ratio of the petriPERM 35 is 2.74 cm²/mland of the petriPERM 50 is 1.96 cm²/ml. Like other gas permeabledevices, the petriPERM products are also inefficient for scale up. Justto perform a 1000 ml culture, at least 100 devices are needed.Furthermore, these devices are not capable of being operated as a closedsystem.

Gabridge (U.S. Pat ent No. 4,435,508) describes a gas permeable cellculture device configured with a top cover like a petri dish, designedfor high resolution microscopy. The depth of the well is based on the“most convenient size for microscopy”, 0.25 inch (0.635 cm). At best,the device is capable of holding medium at a height of 0.635 cm.

Vivascience Sartorius Group has also introduced gas permeable multiplewell tissue culture plates called Lumox Multiwell into the market. Theseproducts are also distributed by Greiner Bio-One. They are available in24, 96, and 394 well formats. The bottom of the plate is made of a 50micron gas permeable film with a very low auto-fluorescence. Wall heightof each well is 16.5 mm for the 24-well version, 10.9 mm for the 96-wellversion, and 11.5 mm for the 384-well version. Maximum working mediumheight for each well are specified to be 1.03 cm for the 24-wellversion, 0.97 cm for the 96-well version, and 0.91 cm for the 384-wellversion. Although medium height is improved relative to traditionalmultiple well plates, it falls within the limits of other static gaspermeable devices.

Fuller et al. (WO 01/92462 A1) presents a gas permeable multiple wellplate that increases the surface area of the lower gas permeablesilicone material by texturing the surface. However, the wall height islimited to merely that of “a standard microtiter plate”, thereby failingto allow an increase in medium height relative to traditional plates.

In general, it would be advantageous if static gas permeable cellculture devices could utilize membranes that are thicker than those usedin commercially available devices. Conventional wisdom for singlecompartment static gas permeable cell culture devices that rely uponsilicone dictates that proper function requires the gas permeablematerial to be less than about 0.005 inches in thickness or less, asdescribed in U.S. Pat. No. 5,686,304. The Si-Culture™ bag is composed ofdi-methyl silicone, approximately 0.0045 inches thick. Barbera-Guillemet al. (U.S. patent application Ser. No. 10/183,132) and Barbera-Guillem(WO 00/56870) state that the thickness of a gas permeable membrane canrange from less than about 0.00125 inches to about 0.005 inches when themembranes comprised suitable polymers including polystyrene,polyethylene, polycarbonate, polyolefin, ethylene vinyl acetate,polypropylene, polysulfone, polytetrafluoroethylene, or siliconecopolymers. Keeping the films this thin is disadvantageous because thefilms are prone to puncture, easily get pinholes during fabrication, andare difficult to fabricate by any method other than calendaring whichdoes not allow a profile other than sheet profile. It will be shownherein how an increased thickness of silicone beyond conventional wisdomdoes not impede cell culture.

Improved static gas permeable devices are needed. If gas permeabledevices were capable of scale up in the vertical direction, efficiencywould improve because a larger culture could be performed in a device ofany given footprint, and more ergonomic design options would beavailable.

Compartmentalized, static gas permeable devices, are another type ofproduct that provides an alternative to traditional culture devices.However, they also are limited in scale up efficiency by medium heightlimitations and excessive gas permeable surface area to medium volumeratios. These types of devices are particularly useful for creatinghigh-density culture environments by trapping cells between a gaspermeable membrane and a semi-permeable membrane. Although notcommercialized, Vogler (U.S. Pat. No. 4,748,124) discloses acompartmentalized device configuration that places cells in proximity ofa gas permeable material and contains non-gas permeable sidewalls. Thecell compartment is comprised of a lower gas permeable material and isbounded by an upper semi-permeable membrane. A medium compartmentresides directly and entirely above the semi-permeable membrane. A gaspermeable membrane resides on top of the medium compartment. Medium isconstrained to reside entirely above the gas permeable bottom of thedevice. The patent describes tests with a cell culture compartmentcomprised of 0.4 cm sidewalls, a medium compartment comprised of 0.8 cmsidewalls, a cell culture volume of 9 ml, a basal medium volume of 18ml, a lower gas permeable membrane of 22 cm², and an upper gas permeablemembrane of 22 cm². That creates a cell compartment medium height of 0.4cm and allows medium to reside at a height of 0.8 cm in the mediumcompartment. Furthermore, there is a high total gas permeable surfacearea to total medium volume ratio of 1.76 cm²/ml. In a paper entitled “ACompartmentalized Device for the Culture of Animal Cells” (Biomat., Art.Cells, Art. Org., 17(5), 597-610 (1989)), Vogler presents biologicalresults using the device of U.S. Pat. No. 4,748,124. The paperspecifically cites the 1976 Jensen et al. and 1981 Jensen papers as the“theoretical basis of operation.” Dimensions for test fixtures describea 28.7 cm² lower and 28.7 cm² upper gas permeable membrane, a cellcompartment wall height of 0.18 cm allowing 5.1 ml of medium to residein the cell compartment, and a medium compartment wall height of 0.97 cmallowing 27.8 ml of medium to reside in the medium compartment. Totalmedium height is limited to 0.18 cm in the cell compartment, 0.97 cm inthe medium compartment, with a high total gas permeable surface area tototal medium volume ratio of 1.74 cm²/ml.

Integra Biosciences markets compartmentalized gas permeable productscalled CELLine™. As with Vogler's device, the cell compartment isbounded by a lower gas permeable membrane and an upper semi-permeablemembrane. However, unlike the Vogler geometry, all medium in the devicedoes not need to reside entirely above the gas permeable membrane. Onlya portion of the basal medium need reside above the semi-permeablemembrane. The patents that cover the Integra Biosciences products, andproduct literature, describe the need to keep the liquid height in thecell compartment below about 15 mm. A ratio of 5 ml to 10 ml of nutrientmedium per square centimeter of gas permeable membrane surface area isdescribed for proper cell support (U.S. Pat. No. 5,693,537 and U.S. Pat.No. 5,707,869). Although the increase in medium volume to cell culturearea is advantageous in terms of minimizing the frequency of feeding, inpractice the medium height above each centimeter of gas permeablesurface area is limited. The commercial design of the devices covered bythese patents demonstrates that they, like the other gas permeabledevices, limit the amount of medium that can reside above the cells.Over half of the medium volume resides in areas not directly above thesemi-permeable membrane in order to reduce the height of medium residingdirectly above the cells. The non-gas permeable sidewalls of the deviceare designed so that when the device is operated in accordance with theinstructions for use, the height at which medium resides above thesemi-permeable membrane in the CELLine™ products is approximately 3.8 cmin the CL1000, 2.6 cm in the CL350, and 1.9 cm in the CL6Well. Whenoperated in accordance with the instructions for use, the height ofmedium residing in the cell culture compartment is 15 mm for the CL1000,14 mm for the CL350, and 26 mm for the CL6Well. The patents describe,and the devices integrate, a gas/liquid interface at the upper surfaceof the medium. Thus, the gas transfer surface area to medium volumeratio is also limited because gas transfer occurs through the bottom ofthe device and at the top of the medium. The gas transfer surface areato medium volume ratio for each device is approximately 0.31 cm²/ml forthe CL1000, 0.32 cm²/ml for the CL350, and 1.20 cm²/ml for the CL6Well.

Bader (U.S. Pat. No. 6,468,792) also introduces a compartmentalized gaspermeable device. Absent sidewalls, it is in the form of a bag. It iscompartmentalized to separate the cells from nutrients by a microporousmembrane. As with the other compartmentalized gas permeable devices,medium height is limited. U.S. Pat. No. 6,468,792 states although mediumheights up to 1 to 2 cm can be achieved in the apparatus, actual heightsneed to be tailored based upon the O2 supply as a function of “mediumlayer in accordance with Fick's law of diffusion.” Since the upper andlower surfaces of the bag are gas permeable, a minimum total gaspermeable surface area to total medium volume ratio of 1.0 cm²/ml isattained when the apparatus is filled to its maximum capacity.

If compartmentalized gas permeable devices were capable of increasingtheir scale up potential in the vertical direction, they would have amore efficient footprint as the magnitude of the culture increases. Astatic, compartmentalized, gas permeable device that accommodatesvertical scale up is needed.

Gas permeable devices that attempt to improve efficiency relative tostatic gas permeable devices have been introduced. The devices operatein a similar manner as the traditional roller bottle and attempt toimprove mass transfer by medium mixing that comes with the rollingaction. However, efficient scale up is not achieved. One reason is that,like static devices, design specifications constrain the distance thatmedium can reside from the gas permeable device walls. This limitsdevice medium capacity. Thus, multiple devices are needed for scale up.

Spaulding (U.S. Pat. No. 5,330,908) discloses a roller bottle configuredwith gas permeable wall that is donut shaped. The inner cylinder walland the outer cylinder wall are in communication with ambient gas. Thegas permeable nature of the walls provides oxygen to cells, which residein the compartment bounded by the inner and outer cylinder walls. Thecell compartment is filled completely with medium, which is advantageousin terms of limiting cell shear. Spaulding states “the oxygen efficiencydecreases as a function of the travel distance in the culture media andeffectiveness is limited to about one inch or less from the oxygensurface.” Thus, the design limits stated by Spaulding include keepingthe distance between the inner cylindrical wall and the outercylindrical wall at 5.01 cm or less in order to provide adequateoxygenation. In that manner, cells cannot reside more than 2.505 cm froma gas permeable wall. That also leads to a gas permeable surface area tomedium volume ratio of about 0.79 cm²/ml. Furthermore, the need to havea hollow gas permeable core wastes space. The device only has aninternal volume of 100 ml of medium for every 5 cm in length, as opposedto 500 ml for a traditional bottle of equivalent length. The mediumvolume limitation makes this device less efficiently scalable than thetraditional roller bottle, because more bottles are needed for a cultureof equivalent volume. Another problem with the device is the use ofetched holes, 90 microns in diameter, for gas transfer. These holes arelarge enough to allow gas entry, but small enough to prevent liquid fromexiting the cell compartment. However, they could allow bacterialpenetration of the cell compartment since most sterile filters preventparticles of 0.45 microns, and more commonly 0.2 microns, from passing.

In a patent filed in December 1992, Wolf et al. (U.S. Pat. No.5,153,131) describes a gas permeable bioreactor configured in a diskshape that is rolled about its axis. The geometry of this deviceattempts to correct a deficiency with the proposal of Schwarz et al.U.S. Pat. No. 5,026,650. In U.S. Pat. No. 5,026,650, a gas permeabletubular insert resides within a cylindrical roller bottle and the outerhousing is not gas permeable. Although it was successful at culturingadherent cells attached to beads, Wolf et al. state that it was notsuccessful at culturing suspension cells. The device is configured withone or both of the flat ends permeable to gas. The disk is limited to adiameter of about 6 inches in order to reduce the effects of centrifugalforce. The inventors state “the partial pressure or the partial pressuregradient of the oxygen in the culture media decreases as a function ofdistance from the permeable membrane”, which is the same thought processexpressed by Jensen in 1976. They also state “a cell will not grow if itis too far distant from the permeable membrane.” Therefore, the width islimited to less than two inches when both ends of the disk are gaspermeable. These dimensional limitations mean that the most medium thedevice can hold is less than 1502 ml. Therefore, more and more devicesmust be used as the culture is scaled up in size. Also, the gaspermeable surface area to medium volume ratio must be at least 0.79ml/cm² and cells must reside less than 1.27 cm from a gas permeablewall. Furthermore, the device does not adapt for use with existinglaboratory equipment and requires special rotational equipment and airpumps.

In a patent filed in February 1996, Schwarz (U.S. Pat. No. 5,702,941)describes a disk shaped gas permeable bioreactor with gas permeable endsthat rolls in a similar manner as a roller bottle. Unfortunately, aswith U.S. Pat. No. 5,153,131, the length of the bioreactor is limited toabout 2.54 cm or less. Unless all surfaces of the bioreactor are gaspermeable, the distance becomes even smaller. Maximum device diameter is15.24 cm. Thus, the gas permeable surface area to medium volume ratiomust be at least 0.79 ml/cm² and cells can never reside more than 1.27cm from a gas permeable wall. Even with the rolling action, this doesnot render a substantial reduction in the gas permeable surface area tomedium ratio relative to traditional static culture bags, and requiresmore and more devices to be used as the culture is scaled up in size.

A commercially available product line from Synthecon Incorporated,called the Rotary Cell Culture System™, integrates various aspects ofthe Spaulding, Schwarz, and Wolf et al. patents. The resulting productsare have small medium capacity, from 10 ml to 500 ml, require customrolling equipment, are not compatible with standard laboratory pipettes,and are very expensive when compared to the cost of traditional devicesthat hold an equal volume of medium. Thus, they have made little impactin the market because they do not address the need for improvedefficiency in a simple device format.

Falkenberg et al. (U.S. Pat. No. 5,449,617 and U.S. Pat. No. 5,576,211)describes a gas permeable roller bottle compartmentalized by a dialysismembrane. The medium volume that can be accommodated by the bottle is360 ml, of which 60 ml resides in the cell compartment and 300 ml in thenutrient compartment. In one embodiment, the ends of the bottle are gaspermeable. U.S. Pat. No. 5,576,211 states the when the end of the bottleis gas permeable, “gas exchange membranes with a surface area of a least50 cm² have been proven to be suitable for cell cultures of 35 ml.”Therefore, the minimum gas permeable surface area to volume ratio is1.43 cm²/ml. In another embodiment, the body of the bottle is gaspermeable, with a surface area of 240 cm². That gas permeable surfaceoxygenates the entire 360 ml volume of medium that resides in thevessel. Therefore, the minimum gas permeable surface area to volumeratio is 0.67 cm²/ml. The diameter of the bottle is approximately 5 cm,and the length of the bottle is approximately 15 cm. Thus, the bottle ismuch smaller than a traditional roller bottle, which has a diameter ofapproximately 11.5 cm and a length up to approximately 33 cm. Althoughthis device is useful for high-density suspension cell culture, itslimited medium capacity fails to reduce the number of devices needed forscale up. Furthermore, it is not suitable for adherent culture becauseit makes no provision for attachment surface area.

Falkenberg et al. (U.S. Pat. No. 5,686,301) describes an improvedversion of the devices defined in U.S. Pat. No. 5,449,617 and U.S. Pat.No. 5,576,211. A feature in the form of collapsible sheathing thatprevents damage by internal pressurization is disclosed. Gas is providedby way of the end of the bottle and can “diffuse into the supplychamber” by way of the gas permeable sheathing. Unfortunately, it failsto reduce the number of devices needed for scale up because the bottledimensions remain unchanged. Furthermore, it remains unsuitable foradherent culture.

Vivascience Sartorius Group sells a product called the miniPERM that isrelated to the Falkenberg et al. patents. The maximum cell compartmentmodule is 50 ml and the maximum nutrient module is 400 ml. Thus, themaximum volume of medium that can reside in the commercial device is 450ml. The small size of the commercial device, combined with the need forcustom rolling equipment, renders it an inefficient solution to thescale up problem.

There exists a need to improve the rolled gas permeable devices so thatthey can provide more medium per device, thereby reducing the number ofdevices needed for scale up. That can be achieved if a decreased gaspermeable surface area to medium volume ratio is present. Anotherproblem is that non-standard laboratory equipment is needed foroperation of the existing devices. The use of standard laboratoryequipment would also allow more users to access the technology.

The prior discussion has focused on design deficiencies that limitefficient scale up in existing and proposed cell culture devices. Inaddition to the previously described limitations, there are additionalproblems that limit scale up efficiency when adherent cell culture isthe objective.

For traditional static devices that rely upon a gas/liquid interface foroxygenation, the adherent cell culture inefficiency is caused by limitedattachment surface area per device. For example, only the bottom of thedevice is suitable for cell attachment with petri dishes, multiple wellplates, and tissue culture flasks. The traditional flask provides a goodexample of the problem. As described previously, a typical T-175 flaskoccupies about 936 cm³. Yet, it only provides 175 cm² of surface areafor adherent cells to attach to. Thus, the ratio of space occupied togrowth surface, 5.35 cm3/cm², is highly inefficient.

Products that attempt to address the surface area deficiency oftraditional flasks are available. Multi-shelved tissue culture flasks,such as the NUNC™ Cell Factory (U.S. Pat. No. 5,310,676) and CorningCellStack™ (U.S. Pat. No. 6,569,675), increase surface area is bystacking polystyrene shelves in the vertical direction. The devices aredesigned to allow medium and gas to reside between the shelves. Thisreduces the device footprint relative to traditional flasks whenincreasing the number of cells being cultured. The profile of themulti-shelved flasks is also more space efficient that traditionalflasks. For example, the space between shelves of the NUNC™ Cell Factoryis about 1.4 cm, as opposed to the 3.7 cm distance between the bottomand top of a typical T-175 flask. The reduced use of space saves moneyin terms of sterilization, shipping, storage, incubator space, anddevice disposal. This style of device also reduces the amount ofhandling during scale up because one multi-shelved device can be fed asopposed to feeding multiple tissue culture flasks. Furthermore, the useof traditional polystyrene is easily accommodated. Unfortunately, thedevice is still sub-optimal in efficiency since each of its shelvesrequires a gas/liquid interface to provide oxygen.

CeilCube® is an adherent cell culture device available from Corning LifeSciences. It is configured in a similar manner to the multiple shelvedtissue culture flasks, but it eliminates the gas/liquid interface. Thedistance between the vertically stacked cell attachment shelves istherefore reduced because gas is not present. That reduces the amount ofspace occupied by the device. However, in order to provide gas exchange,continuous perfusion of oxygenated medium is required. That leads to avery high level of cost and complexity relative to the CorningCellStack™, rendering it inferior for research scale culture.

Static gas permeable devices do not provide a superior alternative tothe NUNC™ Cell Factory, Corning CellStack™, or CellCube®. Cell culturebags and gas permeable cartridges can provide more attachment area thantraditional tissue culture flasks. That is because they could allowcells to be cultured on both the upper and lower device surfaces.However, gas permeable materials that are suitable for cell attachmentcan be much more expensive than traditional polystyrene. Also, even ifboth the upper and lower surfaces of a gas permeable device allowedcells to grow, only a two-fold increase in surface area would beobtained relative to a traditional gas/liquid interface style devicethat occupied the same footprint. Furthermore, the scale up deficienciesthat have been described previously remain limiting.

Fuller et al. (IPN WO 01/92462 A1) presents a new bag that textures thesurface of the gas permeable material in order to allow more surfacearea for gas transfer and cell attachment. However, medium height isalso limited to that of the commercially available bags. That is becausethis bag is fabricated in the same manner as the other bags. Gaspermeable surface area to medium volume ratio becomes even higher thanthat of other bags, and non-uniform medium distribution is present.

Basehowski et al. (U.S. Pat. No. 4,939,151) proposes a gas permeable bagthat is suitable for adherent culture by making the bottom gaspermeable, smooth, and charged for cell attachment. The inner surface ofthe top of the bag is textured to prevent it from sticking to the lowergas permeable surface. This bag only utilizes the lower surface for cellattachment, rendering it only as efficient in surface area to footprintratio as a traditional flask.

To date, guidance is inadequate on how to create a device thateliminates the reliance on a gas/liquid interface and can integrate thescaffold of the multiple layer flasks without the need for perfusion.Static gas permeable devices only allow gas transfer through the bottomand top of the device. Thus, if traditional scaffolds are included, suchas the styrene shelves provided in the multi-shelved tissue cultureflasks, they will have the effect of inhibiting gas exchange at the celllocation. Gas permeable materials should be located in a manner in whichthe attachment scaffold does not prevent adequate gas transfer. How thatbecomes beneficial will be further described in the detailed descriptionof the invention herein.

The need to provide more efficient cell culture devices during scale upis not limited to static cell culture devices, but also applies toroller bottles. Traditional roller bottles function by use of agas/liquid interface. The geometry is a clever way of providing moresurface area and medium volume while occupying a smaller footprint thanflasks and bags. Their universal use provides testimony to the marketdesire for devices that provide more efficient geometry, since thatleads to reductions in the use of inventory space, incubator space,labor, and biohazardous disposal space.

When bottles are used for adherent culture, cells attach to the innerwall of the bottle. Cells obtain nutrients and gas exchange as therolling bottle moves the attached cells periodically through the mediumand gas space. Roller bottle use is not limited to adherent cells. Theyare also commonly used to culture suspension cells. For example, theculture of murine hybridomas for the production of monoclonal antibodyis routinely done in roller bottles. In typical suspension cell cultureapplications, efficiency improvements related to footprint and sizeversus flasks can be attained, the handling simplicity of the rollerbottle is superior to cell culture bags, and the low cost and level ofcomplexity is superior to spinner flasks. Corning®, the leading supplierof roller bottles recommends medium volume for an 850 cm² bottle between170 ml and 255 ml. The actual capacity of the bottle is about 2200 ml.Therefore, although the roller bottle provides advantages for bothadherent and suspension cell culture, it is still very inefficient ingeometry because the vast majority of the roller bottle, about 88%, iscomprised of gas during the culture process. Roller bottles also deviatefrom the simplicity of static devices because ancillary rollermechanisms are required. Furthermore, they subject the cells to shearforce. Those shear forces can damage or kill shear sensitive cells, andare not present in the traditional static devices.

McAleer et al. (U.S. Pat. No. 3,839,155) describes a roller bottledevice configured to allow cells to attach to both sides of paralleldiscs oriented down the length of the bottle. Unlike the traditionalbottle that rolls in the horizontal position, this device tumbles endover end to bring the discs through medium and then through gas. It doesnothing to reduce the volume of gas residing in the bottle. On thecontrary, it states “another advantage of the present invention is thatextremely low volumes of fluid can be used.” It relies entirely upon thepresence of a large volume of gas, which must be perfused, in the bottleto function. The excessive volume of gas that hinders the efficient useof space in traditional bottles remains. Also, shear forces are notreduced.

Spielmann (U.S. Pat. No. 5,650,325) describes a roller bottle apparatusfor providing an enhanced liquid/gas exchange surface. Trays arearranged in parallel within the bottle. The trays allow an increase ofsurface area for culture and are designed to allow liquid to flow overthem as the bottle rotates. In the case of adherent cells, more surfacearea is available for attachment. In the case of suspension cells, theyare stirred “in contact with gas and liquid phases” by the trays. Shearforces remain present. Although this apparatus provides an improvedsurface area, it relies entirely upon the presence of gas in the bottleto provide gas exchange. Thus, it does not address the fundamentallimitation in space efficiency, which is the excessive volume of gasthat must reside in the bottle.

If the roller bottle could be made to allow a vastly improved mediumvolume to gas ratio, it would provide a more economical option becausethe number of devices needed for scale up would be reduced. Since thetypical medium volume for an 850 cm² bottle is 170 ml to 255 ml, but thecapacity is 2200 ml, about a 9 to 13 fold increase in nutrient capacitycould be made available by filling the bottle with medium. To retainsimplicity, a non-complicated method of oxygenating the cultureindependent of a gas/liquid interface would need to exist. Also, foradherent culture, surface area should increase in proportion to theincrease in medium volume. A gas permeable device with thesecharacteristics could lead to a 9-fold to 13-fold reduction in the costof sterilization, shipping, storage, use of incubator space, labor, anddisposal cost. Shear forces on the cells could also be reduced.

For adherent culture, proposed and commercially available rolled gaspermeable devices do not provide a superior alternative to traditionalbottles because they have not integrated traditional attachmentsurfaces. Instead they rely upon small sections of attachment area orbeads. Beads bring a new set of problems to those performing adherentculture. They are difficult to inoculate uniformly, it is not possibleto assess cell confluence or morphology microscopically, and they mustbe separated from the cells that are attached to them if cell recoveryis desired.

Attempts to eliminate the use of beads in gas permeable roller bottleshave been made. Nagel et al. (U.S. Pat. No. 5,702,945), attempts tocreate the ability for the Falkenberg et al. devices to culture adherentcells without beads. One cell attachment matrix is provided in the cellculture compartment at the inner face of the gas membrane. Althoughadherent culture is possible, the bottle dimensions remain unchangedand, due to its small size, it fails to reduce the number of devicesneeded for scale up. Also, oxygen must transfer first through the gaspermeable membrane and then through the cell attachment matrix to reachthe cells. Furthermore, only one layer of cell attachment matrix isavailable, as opposed to the multiple layers of the NUNC™ Cell Factoryand Corning CellStack™. Additionally, microscopic assessment of cellconfluence and morphology is not accommodated.

An improved gas permeable roller bottle is needed. It should be capableof being filled with medium, used in standard roller racks, allowing anincrease in cell attachment area in direct proportion to the increasedmedium volume, and retain the ease of use of the traditional bottle. Itwill be shown herein how this can be achieved.

Singh (U.S. Pat. No. 6,190,913) states that for “all devices that relyon gas-permeable surfaces, scale-up is limited”. A bag is disclosed forresolving the scale up deficiencies of gas permeable devices. Thenon-gas permeable bag integrates medium and gas, in roughly equalproportions. The bag is placed on a rocker plate, and the rocking motioncreates a wave in the medium, which enhances gas transfer. This patentcovers the commercial product, available from Wave Biotech called theWave Bioreactor. Unfortunately, custom rocking and temperature controlequipment must be purchased for the apparatus to function, and the bagdoes not substantially alter the capacity to hold medium. As with gaspermeable bags, the Wave Bioreactor bags are filled with medium to nomore than one half of their carrying capacity. Thus, they limit mediumheight and inherit similar scale up deficiencies as gas permeable bags.

In summary, a need exists for improved cell culture devices and methodsthat bring more efficiency to research scale cell culture, and do notlose efficiency during scale up. Traditional devices that rely upon agas/liquid interface to function are inefficient in terms of labor,sterilization cost, shipping cost, storage cost, use of incubator space,disposal cost, and contamination risk. Those devices include the petridish, multiple well tissue culture plate, tissue culture flask, multipleshelved tissue culture flask, and roller bottle. Gas permeable devicesare also inefficient, and in many cases lose the simplicity of thedevices that require a gas/liquid interface to function. The petriPERMand Lumox multiwell plate gas permeable devices are in the form of theirtraditional counterparts, and inherit the inefficiencies of traditionaldevices. Gas permeable bags are inefficient due to medium heightlimitations, non-uniform medium distribution, use of high gas permeablematerial surface area to medium volume ratios, and the contaminationrisk present during feeding. Gas permeable cartridges are inefficientbecause they have a low height of medium, use a high gas permeablesurface area to medium volume, house a small volume of medium, andrequire a very large number of units to be maintained during scale up.Rolled gas permeable devices are inefficient for scale up because theyhave geometry constraints that limit the distance that the walls can beseparated from each other, require a large number of units during scaleup due to limited medium volume, and often require custom rollingequipment. When adherent culture is desired, traditional devices have avery inefficient device volume to attachment surface area ratio, wastingspace. Static, mixed, and rolled gas permeable devices become even moreinefficient for adherent culture for reasons that include limitedsurface area, the use of beads for increased surface area, lack oftraditional sheet styrene surfaces, and inability to perform microscopicevaluations.

Certain embodiments disclosed herein provide more efficient cell culturedevices and methods, that overcome the limitations of prior devices andmethods, by creating gas permeable devices that can integrate a varietyof novel attributes. These various attributes include gas exchangewithout reliance upon a gas/liquid interface, increased medium height,reduced gas permeable surface area to medium volume ratios, gas exchangethrough the device side walls, cell support scaffolds that are comprisedof traditional materials, and increased gas permeable materialthickness.

SUMMARY OF THE INVENTION

It has been discovered that for gas permeable devices comprised of alower gas permeable material, it can be beneficial to increase mediumheight beyond that dictated by conventional wisdom or allowed incommercially available devices. It is contemplated by the inventorshereof that convection of substrates within cell culture medium plays amore important role than previously recognized. It would appear that thehistoric reliance upon diffusion for mass transfer underestimates thecontribution that convection makes. That would result in underestimatingthe rate of travel of substrates such as glucose and lactate in cellculture medium, and a failure to recognize that medium residing fartheraway from cells than traditionally allowed can be useful to the cells.If the rate of travel of substrates in medium were underestimated,medium residing in areas believed to be too far away from the cellswould incorrectly deemed to be wasted. The logical consequence would beto unnecessarily configure the gas permeable device to hold less mediumthan could be useful to the cells, in order to reduce the space occupiedby the device, making it more economically sterilized, shipped, stored,and disposed of.

In any event, and as an example of how medium residing at a distancebeyond conventional wisdom can be beneficial, tests were conducted inwhich medium height was increased far beyond that suggested previously,or even possible in commercially available static gas permeable devices.Evaluations of a common cell culture application, using murinehybridomas, demonstrated that more cells were able to reside in a givenfootprint of the device by increasing medium height relative toconventional wisdom. This benefit, not previously recognized, allows avariety of cell culture device configurations that provide moreefficient cell culture and process scale up to become available.

The inventive apparatus and methods herein demonstrate that thegas/liquid interface is not necessary for adequate gas exchange when awall of a device is gas permeable, scaffolds are present, and the deviceis operated in a static mode. This eliminates the need for excess devicesize that results from the presence of gas in traditional devices, andallows gas permeable devices to integrate traditional scaffolds. Thisallows a variety of cell culture device configurations that occupy lessspace than prior devices, and makes them more efficient for scale up.Again, it is contemplated by the inventors that the role of convectionmay be a contributing factor.

It has also been discovered that geometric configurations for gaspermeable roller bottles, that contradict the guidance of conventionalwisdom, can successfully culture cells. The new geometry allows thedevice to contain more medium than previously possible, thereby yieldinga geometric shape that improves scale up efficiency. This allows cellculture device configurations to exist that eliminate the wasted spaceof traditional bottles that contain gas for oxygenation, and aresuperior to gas permeable bottles in terms of scale up efficiency.

It has also been discovered that cells can be effectively cultured usingsilicone gas permeable material that is thicker than conventional wisdomadvocates.

These discoveries have made it possible to create new devices andmethods for culturing cells that can provide dramatic efficiency andscale up improvements over current devices such as the petri dish,multiple well tissue culture plate, tissue culture flask, multipleshelved tissue culture flask, roller bottle, gas permeable petri dish,gas permeable multiple well plate, gas permeable cell culture bag,compartmentalized gas permeable devices, and gas permeable rolleddevices.

Certain embodiments disclosed herein provide superior gas permeable cellculture devices, by increasing wall height in order to allow increasedmedium heights and reduced gas permeable surface area to medium volumeratios.

Certain embodiments disclosed herein provide superior cell culturemethods using gas permeable cell culture devices, by increasing mediumheights and reducing gas permeable surface area to medium volume ratios.

Certain embodiments disclosed herein provide superior cell culturedevices, by allowing gas exchange through a sidewall at least partiallycomprised of gas permeable material.

Certain embodiments disclosed herein provide superior cell culturemethods using gas permeable devices, by allowing gas exchange through asidewall at least partially comprised of gas permeable material.

Certain embodiments disclosed herein provide a superior alternative togas permeable multiple well tissue culture plates, by increasing wallheight in order to allow increased medium height and reduced gaspermeable surface area to medium volume ratios.

Certain embodiments disclosed herein provide a superior alternative togas permeable petri dishes, by increasing wall height in order to allowincreased medium height and reduced gas permeable surface area to mediumvolume ratios.

Certain embodiments disclosed herein provide a superior alternative tothe method of cell culture in gas permeable cell culture bags, byincreasing medium height in order to provide more nutrient support andreducing gas permeable surface area to medium volume ratios.

Certain embodiments disclosed herein provide a superior alternative tothe gas permeable cartridges, by increasing wall height in order toallow increased medium heights and reduced gas permeable surface area tomedium volume ratios.

Certain embodiments disclosed herein provide a superior alternative tothe gas permeable roller bottles, by creating a geometry that allowsmedium to reside at a distance from the gas permeable material beyondthat previously possible.

Certain embodiments disclosed herein provide superior gas permeable cellculture devices that can be operated in the horizontal and verticalposition.

Certain embodiments disclosed herein provide a superior alternative tothe compartmentalized gas permeable devices, by increasing wall heightin order to allow increased medium heights and reducing gas permeablesurface area to medium volume ratios.

Certain embodiments disclosed herein provide a superior cell culturemethods using compartmentalized gas permeable devices, by increasingmedium height and reducing gas permeable surface area to medium volumeratios.

Certain embodiments disclosed herein provide superior gas permeable cellculture devices that utilize silicone material for gas exchange, byconfiguring them with silicone that is greater than 0.005 inches thick.

Certain embodiments disclosed herein provide an improved cell culturebag in which the gas permeable material is silicone that exceeds 0.005inches thick.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are obtained from Jensen et al., “Diffusion inTissue Cultures on Gas-permeable and Impermeable Supports”, J. Theor.Biol. 56, 443-458 (1976), FIG. 1A shows FIG. 2, and FIG. 1B shows FIG.3, of this Jensen et al. paper in which D_(c)m is the diffusion constantof medium and the model for steady state values of PO ₂ and PCO ₂ areshown in a gas permeable container.

FIG. 2 is a copy of FIG. 2 from Jensen, “Mass cell culture in acontrolled environment”, Cell Culture and its Applications, AcademicPress 1977, showing a gas permeable cell culture device configured witha low medium height capacity.

FIG. 3 is a copy of FIG. 2 of U.S. Pat. No. 5,686,304, which has beencommercialized as the Si-Culture™ bag (Medtronic Inc.), showing atypical cell culture bag cross-section.

FIG. 4A is an embodiment of a cell culture device with a housingcomprised of a lower gas permeable material, configured to allow a largevolume of medium to reside above its lower gas permeable material. Aremovable lid protects it from contaminants. FIG. 4B is an embodiment ofa cell culture device with a housing comprised of a lower gas permeablematerial, configured to allow a large volume of medium to reside aboveits lower gas permeable material. The container is accessible by septum.FIG. 4C is an embodiment of a cell culture device with the wallscomprised of gas permeable material such that the device can be laid onits side and operated in the non-rolling or rolling position.

FIG. 5 is an embodiment of a gas permeable cell culture device with alower gas permeable material configured to allow cells to distributeevenly about its lower surface and provide gas to the underside of thelower gas permeable material.

FIG. 6 is an embodiment of a gas permeable cell culture deviceconfigured to maintain medium in areas not directly above the cellsbeing cultured, in order to provide additional nutrient support withouta further increase in device profile.

FIG. 7A and FIG. 7B are two views of an embodiment of a gas permeablecell culture device configured so that it can adjust in height as thevolume of medium within it changes, thereby occupying as little space aspossible at each stage of the culture process and allowing thecapability of being sterilized, shipped, stored, and disposed of in aminimum volume condition which reduces the cost of the process.

FIG. 8 is an embodiment of a gas permeable cell culture deviceconfigured in a multiple well format, capable of holding an increasedvolume of medium per well relative to traditional multiple well tissueculture devices, thereby allowing more efficient research scale cultureby increasing the amount of cells present per well, reducing feedingfrequency, and allowing better clone selection possibilities.

FIG. 9A and FIG. 9B are views of embodiments of a gas permeable cellculture device in a multiple well format, configured with a gaspermeable sidewall. The lower surface of each well of the device can becomprised of exactly the same material as traditional tissue cultureflasks. Elimination of the gas/liquid interface as a requirement for gasexchange allows for an increased number of cells per well and/or reducedfrequency of feeding, better use of incubator space, as well as costreductions in sterilization, shipping, storage, and disposal.

FIG. 10A and FIG. 10B show an embodiment of a gas permeable cell culturedevice configured with scaffolds for culturing adherent cells withoutneed of a gas/liquid interface. It is linearly scalable in thehorizontal and vertical direction creating superior efficiency relativeto traditional adherent culture devices. It is capable of culturingcells on either one or both sides of the scaffolds. It can be operatedin either the rolled or in the unrolled state.

FIG. 11 is an embodiment of a gas permeable cell culture deviceconfigured with scaffolds, at least one of which is suitable for optimalmicroscopic cell assessment.

FIG. 12A, FIG. 12B, FIG. 12C, and FIG. 12D show embodiments of scaffoldsconfigured to provide a further increase in surface area, bringing evenmore efficiency to the gas permeable cell culture device.

FIG. 13 is an embodiment of a gas permeable cell culture device withscaffolds and at least one sidewall comprised of gas permeable material.The need for a gas/liquid interface as a means of gas exchange iseliminated, leading to more efficient use space and the related costbenefits in terms of sterilization, shipping, storage, use of incubatorspace, and disposal.

FIG. 14A, FIG. 14B, FIG. 14C, and FIG. 14D show views of an embodimentof a gas permeable cell culture device configured with scaffolds, thelocation of which can be adjusted for benefits that can includeminimizing the use of trypsin, altering the ratio of medium to culturearea, and minimizing shipping, inventory, and disposal space. FIG. 14Eshows a scaffold configured to maintain equal distance between it, andits neighboring scaffolds.

FIG. 15A, FIG. 15B, and FIG. 15C show an embodiment of scaffoldsconfigured such that the distance between each can be altered while thebody of the device remains at a fixed height. This embodiment canprovide benefits that include minimizing the use of trypsin, or alteringthe ratio of medium to culture area, without need to make the body ofthe device change shape.

FIG. 16 is a cross-sectional view of a tubular test fixture used toassess the effect of medium height on cell growth and antibodyproduction. Biological evaluations using this test fixture demonstratedthe benefit of increasing medium height beyond the limits ofconventional wisdom, and the ability to reduce the gas permeable surfacearea to medium volume ratio of prior devices. These surprising resultsallow device configurations not previously contemplated to exist.

FIG. 17 is a cross-sectional view of a test fixture used to assess theability to culture adherent cells in the absence of a gas/liquidinterface by allowing gas transfer through a sidewall of the testfixture. Biological evaluations using this test fixture demonstrated theability to culture cells in the absence of a gas/liquid interface. Thesesurprising results allow device configurations not previouslycontemplated to exist.

FIG. 18 is a cross-sectional view of a test fixture used to assess theability to culture adherent cells in the absence of a gas/liquidinterface by allowing gas transfer through a sidewall of the testfixture. Multiple scaffolds were integrated into the test fixture.Biological evaluations using this test fixture demonstrated the abilityto culture cells in the absence of a gas/liquid interface. Thesesurprising results allow device configurations not previouslycontemplated to exist.

FIG. 19A is a cross-sectional view of a test fixture used to assess theability to seed cells onto the upper and lower surfaces of a scaffold.FIG. 19B shows one scaffold of the test fixture of FIG. 19A. Biologicalevaluations using this test fixture demonstrated the ability to culturecells in the absence of a gas/liquid interface when gas exchangeoccurred through the sidewall of the device, that a low gas permeablematerial surface area to attachment surface area is functional, thatthat a low gas permeable material surface area to medium volume isfunctional, and that cells can be cultured when the device is in theunrolled position or in the rolled position.

FIG. 20 is a cell distribution pattern, as described in Example 4.

DETAILED DESCRIPTION OF THE INVENTION

By configuring gas permeable devices to be capable of holding medium ata height not contemplated in prior cell culture devices or methods,advantages can accrue including reduced handling frequency, labor,sterilization cost, shipping cost, storage cost, use of incubator space,disposal cost, and contamination risk. Reducing the ratio of gaspermeable surface area to medium volume to a ratio not contemplated inprior cell culture devices or methods can also increase cultureefficiency. It allows an increase in medium height without acorresponding increase in device length or width. In the preferredembodiments, provisions are made that allow either medium height toincrease or the ratio of gas permeable surface area to medium volume todecrease. Provisions can also be made that allow both the medium heightto increase and the ratio of gas permeable surface area to medium volumeto decrease.

A wide variety of embodiments for gas permeable devices and methods thatallow medium to reside at heights beyond conventional wisdom arepossible. They can take the form of prior devices, or entirely newforms. If the form is a gas permeable petri dish up to 50 mm indiameter, medium height should preferably exceed 0.36 cm. A preferredwall height is in excess of 6 mm. If the form is a gas permeable petridish greater than 50 mm in diameter, medium height should preferablyexceed 0.51 cm. A preferred wall height is in excess of 12 mm. If theform is a multiple well tissue culture plate with 384 wells or more,medium height should preferably exceed 0.91 cm and preferred well depthis in excess of 11.5 mm; less than 24 wells to less than 384 wells,medium height should preferably exceed 0.97 cm and preferred well depthis in excess of 10.9 mm; 24 wells or less, medium height shouldpreferably exceed 1.03 cm and preferred well depth is in excess of 16.5mm. If the form is a gas permeable cartridge, medium height and wallheight should preferably be greater than 1.27 cm. If in the form of acell culture bag, medium height should preferably reside beyond 2.0 cmin height at the highest point. If the form is a compartmentalizeddevice, and all medium in the device resides entirely above thesemi-permeable membrane, medium height in the nutrient compartmentshould preferably reside 1.0 cm in height above the semi-permeablemembrane. If the form is a compartmentalized gas permeable device,medium height in the nutrient compartment should preferably residebeyond 3.8 cm in height above the semi-permeable membrane.

If it is the design objective to reduce the gas permeable surface areato medium volume ratio relative to conventional wisdom, a wide varietyof embodiments for gas permeable devices and methods are possible. Theycan take the form of prior devices, or entirely new forms. If the formis a gas permeable petri dish up below 50 mm in diameter, the gaspermeable surface area to medium volume ratio should preferably be below2.74 cm²/ml. If the form is a gas permeable petri dish 50 mm or greaterin diameter, the gas permeable surface area to medium volume ratioshould preferably be below 1.96 cm²/ml. If the form is a multiple welltissue culture plate with 384 wells or more, the gas permeable surfacearea to medium volume ratio should preferably be below 1.10 cm²/ml; lessthan 24 wells to less than 384 wells, the gas permeable surface area tomedium volume ratio should preferably be below 1.03 cm²/ml; 24 wells orless, the gas permeable surface area to medium volume ratio shouldpreferably be below 0.97 cm²/ml. If the form is a gas permeablecartridge in which two sides of the cartridge are gas permeable, thesurface area to medium volume ratio should preferably be below 0.79cm²/ml. If in the form of a cell culture bag, the gas permeable surfacearea to medium volume ratio should preferably be below 1.0 cm²/ml. Ifthe form is a compartmentalized device, and all medium in the deviceresides entirely above the semi-permeable membrane, the gas permeablesurface area to medium volume ratio should preferably be below 1.74cm²/ml. If the form is a compartmentalized device, and all medium in thedevice does not reside entirely above the semi-permeable membrane, thegas permeable surface area to medium volume ratio should preferably bebelow 0.31 cm²/ml.

FIG. 4A shows a cross-sectional view of one embodiment of the invention.Gas permeable cell culture device 10 is configured to allow cells 20 toreside upon lower gas permeable material 30. Although FIG. 4A shows gaspermeable cell culture device 10 structured in the style of a petridish, any number of shapes and sizes are possible that allow medium toreside at a height beyond that of conventional wisdom.

Top cover 55 can be removed to allow medium 50 to be conveniently addedand removed, by either pouring or pipetting, to and from gas permeablecell culture device 10. However, access for medium 50 can also be madein any number of ways common to cell culture devices, including by wayof caps, septums, and tubes. In the event that a closed system isdesired, gas permeable cell culture device 10 can be configured withinlet and outlet tubes that can be connected to medium source and wastebags by way of a sterile tubing connection, using equipment such as thatmade by Terumo Medical Corp. (Somerset, N.J.). Septum configurations, orany other techniques known to those skilled in the art, can also be usedto create a closed container. For example, as shown in FIG. 4B, gaspermeable cell culture device 10 can be alternatively configured as aclosed container with septums 65.

In the event that gas permeable cell culture device 10 is to becompletely filled with medium 50, and cells are intended to settle outof medium 50 by gravity, the profile of the top of gas permeable cellculture device 10 preferably allows medium 50 to reside at a uniformheight above gas permeable material 30. This will allow uniform depositof cells onto lower gas permeable material 30, when cellsgravitationally settle from suspension within medium 50. Theconfiguration of FIG. 4B achieves this purpose.

The lower gas permeable material, e.g., material 30, can be anymembrane, film, or material used for gas permeable cell culture devices,such as silicone, fluoroethylenepolypropylene, polyolefin, and ethylenevinyl acetate copolymer. A wide range of sources for learning about gaspermeable materials and their use in cell culture can be used foradditional guidance, including co-pending U.S. patent application Ser.No. 10/460,850 incorporated herein in its entirety. The use of the wordsfilm and membrane imply a very thin distance across the gas permeablematerial, and the inventors have found that the embodiments of thisinvention function when the gas permeable material of the describeddevices and methods is beyond the thickness associated with films andmembranes. Therefore, the portion of the device that contributes to gasexchange of the culture is called a gas permeable material herein.

Those skilled in the art will recognize that the gas permeable materialshould be selected based on a variety of characteristics including gaspermeability, moisture vapor transmission, capacity to be altered fordesired cell interaction with cells, optical clarity, physical strength,and the like. A wide variety of information exists that describe thetypes of gas permeable materials that have been successfully used forcell culture. Silicone is often a good choice. It has excellent oxygenpermeability, can allow optical observation, is not easily punctured,typically does not bind the cells to it, and can be easily fabricatedinto a wide variety of shapes. If silicone is used, it may be less thanabout 0.2 inches, about 0.1 inches, about 0.05 inches, or about 0.030inches in the areas where gas transfer is desired. The best selection ofmaterial depends on the application. For example, Teflon® may bepreferred in applications that will be exposed to cryopreservation. Foradherent culture, in which cells are to attach to the gas permeablematerial, WO 01/92462, U.S. Pat. No. 4,939,151, U.S. Pat. No. 6,297,046,and U.S. patent application Ser. No. 10/183,132 are among the manysources of information that provide guidance.

If silicone is used as a gas permeable material, increasing thicknessbeyond conventional wisdom may expand the options for design, costreduce the manufacturing process, and minimize the possibility ofpuncture. For example, molding a part with a large surface area when thepart must be very thin can be difficult because material may not flowinto the very small gap between the core and the body of the mold.Thickening the part, which widens that gap, can make the molding processeasier. In additional to possible molding advantages, thicker gaspermeable materials also are less likely to puncture or exhibitpinholes.

The height of walls, e.g., walls 40, plays an important role in devicescale up efficiency. Prior static gas permeable devices limit mediumheight. For example, bags provide no walls and instructions limit mediumheight, while cartridge style devices only provide a very low wallheight (e.g. Opticell® cartridges, CLINIcell® Culture Cassettes, andPetaka™ cartridges). An object of this invention is to provide forincreased medium height, thereby increasing device efficiency. Theheight of the walls can dictate how much medium is allowed to reside inthe device. Adding medium provides a larger source of substrates, and alarger sink for waste products. By increasing wall height when moremedium is needed during scale up, the geometry of the device is morecompatible with the shape of incubators, flow hoods, and biohazarddisposal bags. Furthermore, the increase in volume relative to thesurface area upon which cells reside can allow more medium per cell tobe present. That can have the effect of reducing feeding frequency,thereby reducing labor and contamination risk. It can also have theeffect of increasing the number of cells residing per square centimeterof device footprint.

Structuring walls to allow an increase in medium volume can also havethe beneficial effect of diminishing the effects of medium evaporation.Medium evaporation is a problem in cell culture because it alters theconcentration of solutes residing in the medium. Existing gas permeabledevices are prone to such an event because they have a high gaspermeable surface area to medium volume ratio. Attempts to prevent suchan event are described in U.S. patent application Ser. No. 10/216,554and U.S. Pat. No. 5,693,537 for example. However, simply allowing anincrease in the volume of medium in the device can reduce the impact ofevaporation. If prior static gas permeable devices allowed an increasein medium volume to gas permeable surface area ratio, the rate of soluteconcentration change when evaporation is present would be reducedproportionally.

In a preferred embodiment, walls should be capable of allowing medium toreside at a height that exceeds that of devices that rely upon agas/liquid interface and more preferably exceeds that of typical staticgas permeable devices. For example, the height of wall 40 is beyond 3mm, and more preferably beyond 2.0 cm, and will thus provide advantages.By providing users of the device the option of adding more medium to thedevice than prior gas permeable devices, many advantages accrueincluding the ability to house more cells per device, feed the deviceless frequently, and scale the device up without increasing thefootprint. Walls can be comprised of any biocompatible material andshould mate to lower gas permeable material in a manner that forms aliquid tight seal. The methods of mating a lower gas permeable materialto walls include adhesive bonding, heat sealing, compression squeeze,and any other method commonly used for generating seals between parts.As an option, walls and lower gas permeable material can be formed ofthe same material and fabricated as a single entity. For example, ifsilicone is used, walls and the lower gas permeable material could beliquid injection molded, or dip molded, into a single gas permeablepiece. That has the advantage of creating a gas permeable surface forcells to reside upon when a gas permeable cell culture device is stoodvertically as shown in FIG. 4B, or laid on its side as shown in FIG. 4C,which shows gas permeable wall 41 with cells 20 resting thereupon.

Laying certain gas permeable cell culture devices on a side can helpmake optimal use of incubator space as the profile of the device can bereduced when it is too tall for narrowly spaced incubator shelves. Inthe case where it is desirable to have the gas permeable cell culturedevice reside on its side, making the device square or rectangular,instead of circular, will create a flat surface for cells to reside onwhen on its side. That is advantageous as it prevents localized areasfor cells to pile upon each other, potentially causing harmfulgradients. In the case where the device depth and width differ indimension, three alternate surface areas are available for cells toreside upon, and three alternative maximum medium heights exist,depending on the position gas permeable cell culture device is placedin. When the device is structured for operation in these alternatepositions, the surface upon which the device resides is preferablycomprised of gas permeable material. That allows cells that settle bygravity onto this surface to be at optimal proximity for gas exchange.

Walls are preferably configured with enough structural strength thatmedium is retained in a relatively symmetrical shape above gas permeablematerial in order to make most efficient use of lab space, minimizegradient formation within a medium, and allow a uniform deposit of cellsupon a lower gas permeable material during inoculation. It is alsoadvantageous if walls allow visual assessment of color changes in mediumin order to determine pH or contamination status. Walls may beconfigured in a manner that allows a gas permeable cell culture deviceto be easily lifted by hand. When it is desirable for walls to be gaspermeable, and if a separate entity is placed around walls to retainthem in a rigid position, it preferably should not block gas contactwith the majority of walls.

Gas permeable cell culture devices can be configured to function eitherin the static or rolled mode. To do so, gas permeable cell culturedevices should preferably be cylindrical. A cylindrically shaped bodyprovides more volume than a square or rectangular body when the deviceis to be placed in a standard roller rack. However, a non-cylindricalbody shape can still function on a roller rack by attaching a circularhousing around the body. If it is desired to provide users with theoption of device functioning in the vertical, horizontal, or rollingposition, both the bottom and the sidewalls of the gas permeable cellculture device should be comprised of gas permeable material. If thedevice is only to be operated in the horizontal, rolled or unrolled,position, it may be more cost effective and minimize surface area forevaporation if the ends of the device are not comprised of gas permeablematerial.

If a gas permeable cell culture device is configured in a cylindricalshape with a lower gas permeable material, and the walls are comprisedof gas permeable material, it can be stood vertically or rolleddepending on user preference. It can be advantageous to roll gaspermeable cell culture device when maximum mixing will benefit anapplication, such as can be the case when seeking to decrease antibodyproduction time. If this option is desired, the walls of gas permeablecell culture device should be made gas permeable in the same mannerdescribed for lower gas permeable material. Although there are norestrictions on bottle length or diameter, it can be advantageous if thewalls conform to the diameter of standard roller bottles so that gaspermeable cell culture device can function on a standard roller rack.

If it is desirable to reduce cell shear, filling the device entirelywith medium will eliminate gas from the device so that it cannotcontribute to cell shear. The ports can be designed in any number ofways that reduce the risk of contamination as medium fills the deviceentirely. Also, when the device is to be rolled or function on its side,only side surfaces need be comprised of gas permeable material.

The scale up advantages provided by a device that allows medium toreside at a height that exceeds conventional wisdom will become apparentto those skilled in the art, in light of the Examples demonstratingbiological outcomes herein. As an example of scale up efficiency, when agas permeable cell culture device is cylindrical, operated in thevertical position, and the bottom provides for gas exchange, doublingthe diameter increases the volume by a factor of four when the height isheld constant. For example, a device of approximately 4.5 inches indiameter and about 7.7 inches tall, will house about 2 L of medium. Bymaking the device 9.0 inches in diameter, it will house 8 L of medium.By making the device 18.0 inches in diameter, it will house 32 L ofmedium. Thus, culture volume can easily be scaled up while holding keyparameters constant, such as the medium height and gas permeable surfacearea to medium volume ratio. By holding these parameters constant,protocols that are developed in a small volume device are likely toremain unchanged as device volume increases.

When a gas permeable cell culture device is operated in the verticalposition, and suspension cells are being cultured, it is beneficial ifambient gas can make relatively unobstructed contact with the undersideof the lower gas permeable material. For example, in incubators in whichthe shelves are non perforated, gas transfer in and out of the culturecan be limited if the lower gas permeable material makes contact withthe incubator shelf. In the embodiment shown in the cross-sectional viewof FIG. 5, lower gas permeable material support 80 acts to ensure thatlower gas permeable material 30 is in contact with ambient gas bymaintaining a gas compartment 90. In the preferred embodiment, gascompartment 90 is maintained by allowing lower gas permeable materialsupport 80 to make partial contact with lower gas permeable material 30in a manner that does not diminish the amount of gas exchange requiredto support the culture. In addition to allowing exposure to ambient gas,lower gas permeable material support 80 maintains lower gas permeablematerial 30 in a substantially horizontal state such that cells 20 donot pile up in any low points. That would cause diffusional gradientsand limit cell growth relative to a condition in which cells 20 coulddistribute evenly across lower gas permeable material 30. Therefore, adesign objective for lower gas permeable material support 80 may be tocontact lower gas permeable material 30 in as many locations as neededto keep it substantially horizontal while still allowing adequate gascontact with the lower surface of lower gas permeable material 30. Thoseskilled in the art will recognize there are many ways to achieve thisobjective. As shown in FIG. 5, projections 110 achieve this objective.

A “bed of nails” configuration is one way to maintain lower gaspermeable material 30 in a substantially horizontal position whileallowing adequate gas exchange. For example, 1 mm×1 mm squares,distributed evenly and projecting 1 mm from the lower gas permeablematerial support can retain the lower gas permeable material in asubstantially horizontal position. When the projections 110 occupied 50%of the surface of lower gas permeable material support 80 as shown inFIG. 5, this configuration allowed adequate gas exchange to cultureabout 10 to 15 million murine hybridoma cells per square centimeter on asilicone membrane of about 0.004 inches thick. As also shown in FIG. 5,lower gas access openings 100 allow gas to enter and exit gascompartment 90 of lower gas permeable material support 80 by passivediffusion. This allows gas permeable cell culture device 10B to functionin ambient conditions without need of ancillary pumping mechanisms. Feet95 elevate lower gas permeable material support 80, allowing ambient gasto be available to lower gas access openings 100. This information alsois applicable to maintaining a gas compartment around sidewalls when thedevice functions as described on its side in either the rolling ornon-rolling mode. Other possibilities of allowing adequate gas access toa gas permeable material can be utilized. For example, the CELLine™products from Integra Biosciences AG utilize open mesh elevated from alower plastic support by feet to allow gas access to the gas permeablemembrane. U.S. Pat. No. 5,693,537 also provides additional guidance forthis feature.

In the configuration shown in FIG. 5, cap 70 covers medium access port60 to prevent contamination. O-ring 75 ensures that medium 50 will notleak from gas permeable cell culture device 10B, such as when it is inthe horizontal position, completely filled, or accidentally dropped.

In certain embodiments, the medium does not need to reside entirelyabove the lower gas permeable material. A portion of the medium canreside in areas not directly above a lower gas permeable material inorder to reduce the profile of a vertical cell culture device, which maybe desirable for use in incubators with limited distance betweenshelves. The cross-sectional view of FIG. 6 shows an embodimentconfigured for suspension cell culture in which walls 40C are offsetfrom lower gas permeable material 30 in order to decrease the profile ofgas permeable cell culture device 10C when operated in the verticalposition. In this configuration, the ratio of medium volume to surfacearea upon which cells reside can be held constant while the profile ofthe device is reduced in size by simply increasing the width, ordiameter, of gas permeable cell culture device 10C. Care should be takento ensure that cells 20 continue to reside above lower gas permeablematerial 30 during inoculation, feeding, and handling. Interior walls 42achieve this by allowing gravity to keep cells 20 in the area abovelower gas permeable material 30. In a preferred embodiment, the wallsshould be capable of allowing medium to reside at a height above lowergas permeable material 30 that exceeds 3 mm.

FIG. 7A and FIG. 7B show cross-sectional views of a preferred embodimentfor a gas permeable cell culture device that can raise or lower itsheight in response to the volume of medium residing within it. In FIG.7A, medium 50 is added to gas permeable cell culture device 10D andmakes contact with buoyant shoulder 25. In FIG. 7B, medium 50 exerts anupward force on buoyant shoulder 25, causing gas permeable cell culturedevice 10D to rise in height in response to the increasing volume ofmedium 50. In the configuration shown, walls 40D are bellows shaped toallow extension and contraction of the height of gas permeable cellculture device 10D. Buoyant shoulder 25 can be any biocompatiblematerial that is less dense than medium 50. It can also be an integralpart of walls 40. It should be sized to displace the appropriate volumeof medium 50 in order to exert enough force to extend gas permeable cellculture device 10D upward. In this configuration, gas permeable cellculture device 10D only occupies as much space as needed to perform theculture and one product can be the optimal size for a variety ofapplications. For example, the volume of medium suitable for culturinghybridomas may differ from the amount of medium suitable for maintainingpancreatic islets. In that case, gas permeable cell culture device 10Donly need occupy as much space as needed for each application. Also, itallows sterilizing, shipping, storage, incubation, and disposal in theminimum volume condition, thereby reducing the cost of the cultureprocess. Those skilled in the art will recognize that there are manyother ways of altering the device profile other than buoyancy, includinga wide variety of mechanical mechanisms such as those described inco-pending U.S. patent application Ser. No. 10/460,850.

FIG. 8 shows an embodiment for a gas permeable multiple well plate 15,in which the bottom of each well is gas permeable. The properties oflower gas permeable material 30A are the same as those described in theembodiment of FIG. 4A. Although a six well plate is shown, any number ofindividual wells 45 can be present, including the traditional formats ofsix, twenty-four, forty-eight, and ninety-six wells. Walls 40E arestructured to allow medium to reside at a height above lower gaspermeable material 30A that exceeds the wall height of traditionalmultiple well plates, thereby increasing the number of cells that canreside in each well while reducing the footprint relative to traditionalmultiple well plates. For example, murine hybridoma cells typically canreside at a density of 1×10⁶ cells per ml of medium. When the well has adiameter of 8.6 mm, and 2 mm of medium height, 0.12 ml of medium ispresent and about 0.12×10⁶ cells can reside per well. However, if 1 mlof medium could reside in the well by making the wall taller, enoughmedium to support nearly five times as many cells (i.e. 1×10⁶ cells perml) could be present per well, provided that number of cells couldreside upon a gas permeable material with a surface area of 0.58 cm²(i.e. 8.6 mm diameter). Example 1 demonstrates that many more than 1×10⁶murine hybridoma cells can reside on a surface area this size dependingon medium volume. Not only can more medium support more cells, it canallow feeding frequency to be reduced, and reduce the rate at whichevaporation alters medium composition.

Walls can be comprised of any biocompatible material and should mate tothe lower gas permeable material in a manner that forms a liquid tightseal. The methods of mating lower gas permeable material 30A to walls40E are the same as those described for the embodiment of FIG. 4A. Also,as described in the embodiment of FIG. 4A, walls 40E and lower gaspermeable material 30A can be formed of the same material and fabricatedas a single entity. Lower gas permeable material 30A can be supported ina substantially horizontal position as shown in FIG. 5, where lower gaspermeable material support 80 is configured with lower gas accessopenings 100 in communication with gas compartment 90. In the event thatthe span of the bottom of well 45 is small, support may be unnecessarybecause the physical strength of lower gas permeable material 30A canretain it in an adequate horizontal position, depending on the thicknessand physical properties of the gas permeable material. In this case,feet 95A can be used to elevate gas permeable multiple well plate 15 sothat gas transfer is not a problem in an incubator with non-perforatedshelves. Top cover 55A prevents contamination and minimizes evaporation.

FIG. 9A shows a cutaway of a perspective view, and well 45A of FIG. 9Bshows cross-section A-A, of a preferred embodiment for a gas permeablemultiple well plate 16. In this embodiment, the walls of the wells aregas permeable. Although a six well plate is shown, any number ofindividual wells 45A can be present, including the traditional formatsof six, twenty-four, forty-eight, and ninety-six wells. Thisconfiguration may be useful when it is desirable to retain either themicroscopic, attachment surface, or light visibility properties of thetraditional multiple well tissue culture plate. Yet, by making each well45A deeper than the maximum depth of traditional multiple well platesused for cell culture, more medium can be made available for culture andthe gas permeable nature of the walls will allow proper gas exchange ofthe culture, rendering the location of the gas/liquid interfaceinconsequential. Non-gas permeable bottom 31 mates to gas permeable wall41 in a liquid tight manner. There are a number of ways to achieve thisobjective. For example, the diameter of non gas permeable bottom 31 canslightly exceed the diameter of gas permeable wall 41, causing gaspermeable wall 41 to apply a force against non gas permeable bottom 31,thereby creating a liquid tight seal. Gas permeable wall 41 can have anyof the properties as described for the gas permeable material of FIG.4A. However, in a preferred embodiment gas permeable wall 41 iscomprised of silicone because of its ability to be easily fabricated byliquid injection molding, and its capacity to stretch and provide aliquid tight seal against non-gas permeable bottom 31. Non-gas permeablebottom 31 can be any plastic commonly used in traditional multiple welltissue culture plates, or any other cell attachment material known tothose skilled in the art.

It may be less expensive to fabricate each well of gas permeablemultiple well plate 16 out of gas permeable material, including the wellbottom, thereby eliminating the seal joint. Then, if adherent culture isdesired, a suitable scaffold can be placed at the bottom of the well.Care should be taken to ensure optical clarity if microscopic evaluationis desired. Any cell attachment surface known to those skilled in theart of cell culture can be placed in the wells. If the cell attachmentsurface is buoyant, making it a press fit into the well can keep it inthe desired position. Many other methods of retaining it in position arealso possible.

FIG. 10A and FIG. 10B show cross-sectional views of one embodiment of agas permeable cell culture device that utilizes space more efficientlywhen culturing adherent cells. Scaffolds 120 reside within gas permeablecell culture device 10E. Sidewalls 40F are comprised of a gas permeablematerial, thereby allowing gas exchange through the sides of the device.In this manner, gas permeable cell culture device 10E is not limited inheight, as scaffolds 120 can be scaled uniformly as height increases.Allowing more cells to be cultured is simply a matter of making thedevice taller, adding more scaffolds 120. In the preferred embodiment,the distance between each scaffold 120 is kept constant during scale up.For example, by configuring scaffolds 120 to have spacers 135, they canbe kept an equal distance apart and retained parallel to the bottom ofgas permeable cell culture device 10E, making scale up in the verticaldirection linear. Pipette access opening 125 allows pipette accessthroughout gas permeable cell culture device 10E and provides an openingto vent gas as medium is added. Although shown in the center, pipetteaccess can be in any location, or can be eliminated entirely in favor ofany other form of liquid handling such as needles and septum. In FIG.10A, cells 20A are well suspended in inoculum 130 and will distributeevenly about the upper surface of each scaffold 120, since the volume ofinoculum 130 above each scaffold 120 is equal. If both sides of scaffold120 are intended to culture adherent cells, inoculation can occur in twosteps by inoculating one side of scaffolds 120 first, as shown in FIG.10A. After cells have gravitationally deposited and attached onto thesurface of scaffolds 120, gas permeable cell culture device 10E is thenre-inoculated, rotated one hundred eighty degrees to expose the oppositeside of scaffolds 120, and cells 20A are allowed to settle and attach tothe exposed surface of scaffolds 120 as shown in FIG. 10B.

Post cell attachment, typically less than 24 hours to seed one side ofthe scaffolds, the device can be operating in any static position thatis convenient, such as vertical, inverted, or on its side. If desired,it can be rolled if a user desires a format more similar to a rollerbottle. Unlike traditional devices, the device can be filled completelywith medium, as gas exchange occurs by way of the gas permeable wallsand the need for a gas/liquid interface is not present.

In this manner, the device is more efficient in its use of space thantraditional devices since gas does not need to be present in the devicefor gas exchange of the culture. The limiting factors to the number ofcells that can be cultured in the device include the amount of scaffoldsurface area, the volume of medium present, the gas permeability andthickness of the material used for the device walls, the distance thecells reside from the gas permeable walls of the device, and the type ofcells being cultured.

Understanding the importance of the medium volume to scaffold area ratiowhen designing the gas permeable cell culture device can help predictthe output of the device. For instance, if the culture has beenhistorically conducted in a roller bottle, the medium volume to surfacearea of the roller bottle culture can be replicated in the gas permeablecell culture device. For example, if the existing culture had beenperformed in a traditional 850 cm² roller bottle using 150 ml of medium,and the gas permeable cell culture device was to have the same outsideshape as the traditional bottle, the medium volume to surface area ratiocould be held constant. A gas permeable cell culture device constructedin the shape of the traditional 850 cm² roller bottle can hold about2200 ml of medium. That is a 14.67 fold increase in medium volumerelative to the 150 ml medium volume of the traditional roller bottle.Therefore, a 14.67 fold increase in surface area, which is 12,470 cm²,is needed to keep an equivalent medium to surface area ratio. Thus, whena gas permeable cell culture device contains 2200 ml of medium and has ascaffold surface area of 12,470 cm², it can be expected to culture thesame number of cells as about fifteen traditional 850 cm² roller bottlesthat normally operate with 150 ml per bottle, and the feeding frequencyshould be about the same.

The ability to microscopically assess cell confluence is useful for manyapplications. If the lowest scaffold comprises the bottom of gaspermeable cell culture device, it can be used to assess cell confluence.When the volume of medium residing above each scaffold is equal duringinoculation, the amount of cells residing upon any of the scaffolds willbe relatively equal throughout the culture. Thus, one scaffold can berepresentative of the others. For some microscopes, the ability tophysically move the lowest scaffold into a position that allowsmicroscopic observation by inverted scopes can allow a better assessmentof confluence and morphology. The configuration shown in thecross-sectional view of FIG. 11 shows how this can be achieved. If wall4 GH is flexible, as will be the case when it is fabricated out of manygas permeable materials such as silicone, it can be pleated to allowmovement of the lowest scaffold 120 relative to gas permeable cellculture device 10F. Microscopic evaluation can also be made possible bymanufacturing gas permeable cell culture device 10F in the fixedposition shown in FIG. 11, thereby eliminating the need to move thelowest scaffold 120 relative to gas permeable cell culture device 10F.

Although the scaffolds shown in FIG. 10A, FIG. 10B, and FIG. 11 areflat, they can be any geometric shape that allows cells to attach. Forexample, corrugating the surface can increase surface area relative to aplanar surface, thereby increasing the amount of adherent cells that canreside upon a given scaffold. FIG. 12A shows a perspective view of around corrugated scaffold 120A, which is corrugated in a lineardirection. FIG. 12B shows cross-sectional view A-A. FIG. 12C shows aperspective view of round corrugated scaffold 120B, which is corrugatedin the circular direction, and FIG. 12D shows cross-sectional view B-B.For some applications in which a high rate of gas transfer is needed tosupport highly active cells, the configuration of FIG. 12A may besuperior because the channels for gas transfer are unobstructed by theedge of the scaffold, as is the case for the configuration of FIG. 12C.For other applications in which the gas permeable cell culture device isrolled, the configuration of FIG. 12C may be superior because the shapewill minimize turbulence, which could cause cell shear.

The configurations, methods of microscopically viewing, and methods ofincreasing scaffold area such as those described in FIG. 10A, FIG. 11,and FIG. 12, can be integrated into a multiple well format. Theseconfigurations are completely scalable in size. FIG. 9B shows highsurface area well 46, configured with multiple scaffolds 120 maintaineda predetermined distance apart by spacers 135. Making them the size ofthe wells of a typical traditional multiple well tissue culture platewill allow a substantial increase in the number of adherent cellspresent per well. The walls 41A are preferably gas permeable.

FIG. 13 shows a cutaway view of configuration for a gas permeable cellculture device that is useful for culturing cells in a format similar tothat of a tissue culture flask. In this embodiment, at least one wall ofthe device provides gas transfer. This device is beneficial because itallows the gas permeable cell culture device to retain the sameattributes as the traditional tissue culture flask while achieving amore compact use of space. The desirable attributes include easy mediumdelivery and removal by way of pouring or pipetting, microscopicobservation capability, the ability to easily see color changes in themedium that may indicate contamination or pH changes, and capability fordevice stacking to make the most efficient use of shipping, storage, andincubator space. However, it is superior to the tissue culture flaskbecause the gas/liquid interface required for tissue culture flaskoperation is eliminated and one or more scaffolds can be present. In theembodiment shown, gas permeable cell culture device 12 is comprised of aliquid tight enclosure with at least one gas permeable wall 200. Mediumaccess port 60A is covered by cap 70A. Scaffolds 120D are orientedparallel to each other, with a gap between them to allow inoculum andmedium to reside in between each scaffold 120D. Preferably, scaffolds120D are positioned an equal distance apart to allow an equivalentvolume of inoculum or medium to reside above each of them. The gaspermeable material of gas permeable wall 200 has the same attributes asthose described for lower gas permeable material 30 of the embodimentshown in FIG. 4A. In the preferred embodiment, scaffolds 120D haveidentical material characteristics as those present in traditionaltissue culture flasks. Top wall 201 and bottommost scaffold 120D areclear, allowing visual assessment of medium color as well as microscopicevaluation of the bottom scaffold 120D. Making the rear or other wallsgas permeable can create more gas transfer capacity. That will have theeffect of making it possible to further increase the footprint of gaspermeable cell culture device 12. For example, if the gas transfercapacity of gas permeable wall 200 supports cells residing uponscaffolds 120D of a five inch width, making the opposing side wall gaspermeable will allow enough gas transfer capacity when scaffolds 120Dthat are ten inches wide. Gas permeable cell culture device 12 isunlimited in scale up capacity in the vertical direction.

FIG. 14A through FIG. 14E show another method of utilizing space moreefficiently when culturing cells. In this configuration, scaffolds 120Ereside within gas permeable cell culture device 10G, which is capable ofexpanding in volume as medium 50 is added. In FIG. 14A, gas permeablecell culture device 10G is in a collapsed position under its own weight.That allows efficient use of space for shipping, sterilization, andstorage prior to use. Scaffolds 120F are as close to each other aspossible. Each scaffold 120F is molded with spring arms 145 that exertforce on the lower, neighboring scaffold 120F. Spring arms 145, incompression, want to distend, but cannot because the weight of the upperportion of gas permeable cell culture device 10G exceeds the springforce. In FIG. 14B, gas permeable cell culture device 10G has risen inheight in response to the force exerted by the addition of inoculum 130Aagainst buoyant shoulder 25A. The displacement of inoculum 130A bybuoyant shoulder 25A exerts an upward force that, when combined with thespring force of spring arms 145K, exceeds the weight of the upperportion of gas permeable cell culture device 10G. Scaffolds 120Fseparate and maintain an equal distance from each other due to the forceexerted by spring arms 145 against their lower, neighboring scaffold120F. Maintaining an equal distance from each other is particularlybeneficial during inoculation, when the volume of inoculum 130A residingdirectly above each of scaffolds 120F dictates the amount of cells thatwill be deposited onto each of scaffolds 120F. By allowing an equalvolume of inoculum 130A to reside above each scaffold 120F, and equalnumber of cells can reside upon each scaffold 120F. In FIG. 14C, gaspermeable cell culture device 10G has risen in height again relative toFIG. 14B in response to the addition of medium 50 as the cell populationexpands and nutrient demand increases. Scaffolds 120F further separateand maintain an equal distance from each other due to the force exertedby spring arms 145 against their lower, neighboring scaffold 120F. Theconstant distance between each of scaffolds 120F ensures a constantmedium 50 volume to surface area ratio at all cell locations, reducingthe potential for gradient formation. In FIG. 14D, gas permeable cellculture device 10G has collapsed due to the removal of medium 50 andloss of upward force of buoyant shoulder 25A. It is now at an efficientsize for disposal. In the event that adherent cell recovery is needed,allowing gas permeable cell culture device 10G to collapse is beneficialwhen removing medium 50 and adding trypsin. In this manner, only a smallvolume of trypsin is needed to recover cells. Those skilled in the artwill recognize that many other methods of altering the height of gaspermeable cell culture device 10G can be applied.

Spring arms 145 can be molded directly into scaffold 120F, as shown inthe perspective view of FIG. 14E. A spring arm 145, preferably locatedin at least three places, ensures that scaffold 120F remains in planeand parallel to its neighboring scaffold 120F. Although any materialconducive to cell attachment is acceptable, a preferred material forscaffold 120F is polystyrene, which is quite brittle. Therefore, careshould be taken to ensure that spring arms 145 are configured inaccordance with good molded part design to prevent cracking understress. Techniques for low stress part design are well known to thoseskilled in the art of plastic part design.

Moving the position of the scaffolds independent of the height of thegas permeable cell culture device may be desired. For example, this maybe practical when it is more economical to configure the gas permeablecell culture device with non-extending walls, but the application canstill benefit by altering the medium volume to surface area ratio aboveeach of the scaffolds during culture. FIG. 15A through FIG. 15C show oneembodiment for achieving that objective. For clarity, only a portion ofthe gas permeable cell culture device is shown. In the top view of aportion of a gas permeable cell culture device shown in FIG. 15A, threeelevation posts 160 are positioned to travel up each of three ramps 150in order to change the distance between the scaffolds.

The method of varying the distance between scaffolds can best beunderstood by reviewing FIG. 15B and FIG. 15C. FIG. 15B showscross-section A-A of FIG. 15A. As shown in FIG. 15B, two scaffolds 120Gare shown the position in which the distance between them is at aminimum. Ramp 150 emanates from the top of scaffold 120G and elevationpost 160 emanates from scaffold locator screw 170. Elevation post 160has not begun travel up ramp 150. It can be seen that the minimumdistance between scaffolds is dictated by the height of ramp 150, whichmakes contact with the underside of the scaffold 120G that resides aboveit. Referring to FIG. 15C, scaffolds 120G are in the position of maximumdistance between them. Scaffold locator screw 170 has been rotated inthe direction of rotation arrow 180, causing elevation post 160 to riseup ramp 150 and elevate the scaffold 120G residing above it. Whenelevation post 160 resides at the highest point of ramp 150L, themaximum distance between scaffolds 120L is attained as is equal to theheight of ramp 150 plus the height of elevation post 160. Scaffolds 120Gshould be prevented from rotating when scaffold locator screw 170 isturned, thereby allowing ramp 150 to remain in a fixed position whileelevation post 160 travels up it. This can be achieved by matingscaffolds 120G to the interior of the gas permeable cell culture devicewall by way of a tongue and groove arrangement. As best shown in the topview of a scaffold of FIG. 15A, tongue 212 emanates from gas permeablewall 40H and mates to groove 215 in each scaffold 120G. Not only doesthis prevent rotation of scaffold 120G during rotation of locator screw170, it also prevents gas permeable wall 40H from pulling away fromscaffold 120G. In this manner, the shape of the gas permeable cellculture device is retained. Locator screw 170 can be configured to allowa sterile pipette tip to rotate it, thereby preventing contamination ofthe device and allowing the use of standard laboratory tools torearrange the distance between scaffolds.

The invention will be further described with reference to the followingnon-limiting Examples.

EXAMPLES Example 1 The Effect of Medium Height Upon Cell Growth andAntibody Production

Evaluations were conducted in order to assess the impact of alteringmedium height upon cell growth and antibody production in a devicecomprised of a lower gas permeable material. The effect of altering thegas permeable material surface area to medium volume ratio was alsoassessed. Single compartment test fixtures configured with a lower gaspermeable materials and the capacity to hold medium at heights beyondconventional wisdom were compared to single compartment control testfixtures that held medium at a height within the bounds of conventionalwisdom. Comparisons were made relative to the 1.6 cm medium heightlimits specified for the Si-Culture bag (U.S. Pat. No. 5,686,304).Control test fixtures were configured to house medium at a height of 1.6cm, and the gas permeable material used for of all test fixturesconsisted of gas permeable material obtained from actual Si-Culture™bags.

Tubular test fixtures 105 were constructed as shown in FIG. 16. Walls401 were machined out of Ultem 1000 (high temperature polycarbonate)cylindrical stock, resulting in a tube with an inner diameter of 1.00inch and an outer diameter of 1.50 inch. The thick walls ensured thatgas transfer through the walls would not assist the cultures. Lower gaspermeable material 30A was fabricated from 0.045 thick sheets ofsilicone removed from Si-Culture™ bags and secured in a liquid tightmanner to the bottom of the machined tube yielding a 5.07 cm² growtharea for cells 20B to reside upon. Lower gas permeable material support80M was also machined out of Ultem 1000. Lower gas permeable material30A was held in the horizontal position by mesh 115 which maintained gascompartment 90A. Mesh 115 was comprised of 0.020 inch diameter strandsat 16 strands per inch. Lower gas access openings 100A allowed gaseouscommunication with the 5% CO₂, 95% R.H., and 37 C ambient environment.Comparisons were made for the capacity of the devices to grow cells 20Bwhen differing amounts of medium 50A resided within the test fixture.Cap 70B, secured tightly to walls 401, protected tubular test fixture105 from contamination. Tests compared the results when medium 50Aresided at a height of about 1.6 cm, 3.2 cm, 5.6 cm, 10.2 cm, 15.3 cm,and 20.4 cm above the cells. Medium 50A consisted of HycloneHyQSFM4MAb-Utility supplemented with 10% Hyclone FBS. Cells 20B weremurine hybridoma cells secreting IgG, inoculated at a seeding density of0.76×10⁶ per cm² of lower gas permeable material 30A. Ambient conditionswere 5% CO₂, 95% R.H., and 37 C. Periodic cell counts and monoclonalantibody production measurements by ELISA were taken. TABLE 1 shows theresults.

TABLE 1 Medium Height Affect Upon Cell Growth and Antibody ProductionGas permeable Height of surface Time to medium area to Maximum maximumVolume above gas medium Maximum live cells per Mab amount of Mab per mlof permeable volume live cells cm² of gas produced per mab of mediummedium material ratio per device permeable test fixture producedconsumed (ml) (cm) (cm²/ml) (×10⁶) material (×10⁶) (ug) (days) (ug/ml)8.1 1.60 0.63 29.7 5.85 2742 9 339 16.2 3.20 0.31 51.0 10.05 7395 12 45725.8 5.09 0.20 59.1 11.65 10673 18 374 51.7 10.20 0.10 61.1 12.05 1525215 295 77.6 15.31 0.07 67.2 13.25 23044 22 299 103.4 20.39 0.05 86.417.04 32881 25 318

Dividing each parameter measured in any given test fixture by thecorresponding parameter of the test fixture representing conventionalwisdom (i.e. 1.6 cm) clearly shows the advantages of allowing medium toreside at heights beyond conventional wisdom. Gas permeable surface areato medium volume ratio is determined by dividing the ratio of the testfixture by the ratio of the Si-Culture™ bag when it contains medium at aheight of 1.6 cm (i.e. 1.25 cm²/ml). TABLE 2 presents the data of TABLE1 in this manner.

TABLE 2 Normalized data Normalized Normalized by by height of Normalizedgas permeable Normalized Normalized Normalized medium by surface area toby Mab by Mab per by time to Normalized above gas maximum medium volumeproduced ml of attain by footprint permeable live cells per ratiorelative to per test medium maximum of space membrane deviceSi-Culture ™ bag fixture consumed Mab amount occupied 1.00 1.00 50% 1.001.00 1.00 1.00 2.00 1.72 25% 2.70 1.35 1.50 0.50 3.18 1.99 16% 3.89 1.112.00 0.28 6.38 2.06 8% 5.56 0.87 1.67 0.16 9.57 2.26 6% 8.40 0.88 2.500.10 12.75 2.91 4% 11.99 0.94 2.83 0.08

The data of TABLE 2 clearly shows the advantages of altering thegeometry of gas permeable cell culture devices to allow more medium toreside above the cells. For example, the last row shows that when thedevice is allowed to hold medium at a height that is 12.75 times greaterthan the traditional cell culture bag, it is capable of culturing 2.91fold more cells per cm² of floor space occupied, producing 11.99 timesmore monoclonal antibody (Mab) with only a 2.83 fold increase in thetime to complete production. Also, when the gas permeable materialsurface area to medium volume ratio is compared to that of theSi-Culture™ bag, dramatically reduced ratios are possible. Cultures wereeffectively grown even when the ratio was only 4% of that used by theSi-Culture™ bag. That allows a wider variety of device configurations toexist, including allowing the device footprint to remain fixed as mediumheight is increased. It also minimizes the effects of evaporation, asmore medium is present per cm² of gas permeable surface area.

Importantly, this data demonstrates that device footprint can remainsmall as the culture is increased. TABLE 3 shows the surface area of thedevice footprint needed to house the volume of medium residing in thetest fixtures. The first row shows the medium volume in the testfixture. The second row shows the footprint area of the test fixture,which remained fixed as more and more medium was added. The third rowshows the footprint surface area that would be required in a typical bagto hold the volume of medium residing in the test fixture. In this case,the footprint is shown for a Si-Culture™ bag when it contains the volumeof row one at the manufacturers recommended medium height of 1.6 cm. Thefourth row shows the difference in footprint area. For example, when thetest fixture contains 103.4 ml of medium, the Si-Culture™ bag whenoperated according to manufacturers recommendation would have afootprint of 64.6 cm², but the test fixture only has a footprint of 5.1cm². Thus, the test fixture that allowed medium to reside at a height of20.39 cm only needed a footprint of 8% of that needed for a Si-Culture™bag to produce roughly the same amount of Mab.

TABLE 3 Much more efficient use of floor space. Volume of medium in 8.116.2 25.8 51.7 77.6 103.4 device (ml) Test fixture footprint (cm²) 5.15.1 5.1 5.1 5.1 5.1 Bag footprint with medium at 5.1 10.1 16.1 32.3 48.564.6 1.6 cm high (cm²) Ratio of test fixture footprint 100% 50% 32% 16%11% 8% to bag footprint (%)

Benefits relative to all of the conventional configurations arenumerous. The unwieldy shape of traditional cell culture bags can beavoided allowing a wide variety of benefits to accrue related to moreefficient use of incubator space, easier medium delivery and removal,and reduced contamination risk. The small volume of medium present ingas permeable cartridges can be increased substantially by making themtaller, and reducing the ratio of gas permeable membrane to mediumvolume capacity. That has the effect of allowing fewer units to beneeded during scale up. For traditional gas permeable formats of thepetri dish and multiple well plate, more cells can reside per unitwithout increasing the footprint of the devices, or the number ofdevices needed, and the frequency of feeding can be reduced. Minimizedevaporative effects can be achieved in all configurations because thegas permeable surface area to medium volume ratio can be significantlyreduced.

Example 2 Effect of Thickness of Gas Permeable Silicone on Cell Growth

Conventional wisdom, as dictated by U.S. Pat. No. 5,686,304 and U.S.patent application Ser. No. 10/183,132, and the design of commerciallyavailable gas permeable products that use silicone, dictates thatsilicone thickness of greater than 0.005 inches should not be used.However, increasing the thickness is advantageous from a manufacturingand product reliability standpoint. Therefore, evaluations wereconducted to assess the impact of the thickness of a lower silicone gaspermeable material on cell growth. The material thickness ofconventional wisdom was compared to the same material at increasingthickness.

Tubular test fixtures were constructed as shown in FIG. 16. Walls weremachined out of Ultem 1000 (high temperature polycarbonate) cylindricalstock, resulting in a tube with an inner diameter of 1.00 inch and anouter diameter of 1.50 inch. Four distinct thickness configurations oflower gas permeable material were created from sheets of siliconeremoved from Si-Culture™ bags. Lower gas permeable material 30A was madeinto double, triple, and quadruple layers, formed by adhering thesilicone sheets together using UV curing silicone glue distributedevenly about the face and sheets were laminated together leaving no airgaps between them. Post curing, the laminated sheets and a single sheetcontrol were secured in a liquid tight manner to the bottom of themachined tube yielding a 5.07 cm² growth area for cells to reside upon.Tests were conducted in triplicate. Lower gas permeable material 30A washeld in the horizontal position by lower gas permeable material support80, configured as described in Example 1. Tests compared the resultswhen medium resided at heights of 20.4 cm above the cells. Mediumconsisted of Hyclone HyQSFM4MAb-Utility supplemented with 10% HycloneFBS. Murine hybridoma cells were inoculated at a seeding density of4.3×10⁶ live cells per square cm of lower gas permeable material.Ambient conditions were 5% CO₂, 95% R.H., and 37C. Periodic cell countsand glucose measurements were taken. TABLE 4 shows the results.

TABLE 4 Effect of Thickness of Gas Permeable Silicone on Cell GrowthMembrane Normalized: Normalized: Thickness Maximum viable cells MembraneMaximum viable (in) per cm² (×10⁶) Thickness cells per cm² 0.0045 15.21.00 1.00 0.016 15.5 3.56 1.02 0.024 13.49 5.33 0.89 0.033 12.0 7.330.79

The data was normalized by referencing it against the data collected forthe single 0.0045 inch thick sheet that represents conventional wisdom.It can clearly be seen that the effect of dramatically increasingthickness does not have a significantly negative impact on the capacityto support cell growth. When the material thickness was increased aboutfour-fold, from 0.0045 inch to 0.016 inch, there was no affect upon cellgrowth. When the silicone membrane thickness was increased 5.33 fold,from 0.0045 inch to 0.024 inch, the growth capacity was diminished byonly 11%. Likewise, a 7.33 fold increase in thickness beyondconventional wisdom resulted in growth capacity being diminished by only21%. In many cell culture applications, such as hybridoma culture formonoclonal antibody production, 79% viability is routinely accepted. Forexample, in the CELLine™ products, hybridoma viability is commonly at50%, as described in the operating instructions. Thus, device design canaccommodate thicker silicone walls without a dramatic reduction inperformance. Fabrication and functional improvements may result fromincreasing the thickness, such as simplified liquid injection molding orless pinhole potential. In summary, it is possible to design a highlyfunctional cell culture device with thicker walls than previouslybelieved possible.

Example 3 The Ability to Culture Cells at a High Liquid Height in aRolled and Unrolled Device

Evaluations were conducted to assess the advantages that could beobtained by configuring gas permeable cell culture devices in ways thatdiffer from conventional wisdom. Two general formats were evaluated, 1)unrolled gas permeable devices and 2) rolled gas permeable devices. Inthe unrolled gas permeable device configuration, medium height was wellbeyond the limits imposed by conventional wisdom. The ratio of gaspermeable surface area to medium volume was reduced far below that ofconventional wisdom. In the rolled gas permeable device configuration,medium was allowed to reside farther away from the gas permeable wall,and more medium was allowed to reside per device, than that of the stateof the art gas permeable rolled bottles.

The production of monoclonal antibody is a common application in cellculture bags and roller bottles. A traditional 850 cm² roller bottlefunctioned as a control. Test fixtures were constructed in accordancewith the embodiments shown in FIG. 4, and dimensionally configured tohave the same dimensions as a traditional 850 cm² Corning® rollerbottle. The gas permeable material was the same as that of theSi-Culture™ bag, as further defined in U.S. Pat. No. 5,686,304. The gaspermeable surface area of non-rolled test fixture was limited to that ofthe bottom surface of the fixture, and was 98 cm². The sidewalls werenot gas permeable. The gas permeable surface area of the rolled testfixture was limited to that of the entire cylindrical sidewall surfaceof the fixture, and was 850 cm², and the ends were not gas permeable.Medium consisted of Hyclone SFM4MAb, supplemented with 2.5% Hyclone FBS.Each test fixture was inoculated with a cell density of 0.04×10⁶ murinehybridoma cells per ml of medium used. The test fixtures each received2050 ml of medium. Ambient conditions were 5% CO₂, 95% R.H., and 37C.

The traditional roller bottle received 255 ml of medium, the maximumamount of medium recommended for use in roller bottles. The presence ofantibody was determined by ELISA. TABLE 5 shows the results.

TABLE 5 Effect of rolling versus standing on antibody production timeMaximum amount Time to reach of antibody maximum Test Fixture Styleproduced (mg) production Unrolled Novel Device 289 16 Rolled NovelDevice 302 13 Traditional Roller Bottle 33 13

TABLE 5 shows how the rolled and the non-rolled gas permeable testfixtures, which occupied the same amount of space as the traditionalroller bottle control, were able to produce about nine times as muchantibody. TABLE 5 also demonstrates how the rolled gas permeable formatcan be used to decrease the amount of time needed to generate antibodyrelative to its standing gas permeable counterpart. A 20% reduction intime, three days, was attained. Importantly, both the roller andunrolled formats can create a at least a nine fold improvement inefficient geometry in terms of space, leading to reduced cost ofsterilization, shipping, storage, labor, incubator space, and disposalwhen compared to the traditional roller bottle.

The results also clearly demonstrate the advantage obtained byconfiguring gas permeable devices in ways that depart from conventionalwisdom. The height of medium in the unrolled test fixture was about 20.9cm, over ten times the highest recommended height of traditional cellculture bags. Had the device been structured with 2.0 cm of mediumheight, it would have needed a footprint of 1025 cm² to house anequivalent volume of medium, which is over ten times the footprint ofthe unrolled test fixture.

Benefits of geometry of the rolled gas permeable device were numerous.The rolled test fixture contained a volume of medium nearly eight timesthe maximum volume of medium recommended for traditional roller bottles(255 ml), over four times the medium volume of Rotary Cell CultureSystem™ from Synthecon Inc., nearly five times the medium volume of theMiniPERM, and well beyond that allowed in the patent proposals ofSpaudling, Schwarz, Wolf et al., and Falkenberg et al. Also, mediumresided up to 5.6 cm from any portion of the gas permeable wall of thetest fixture, over double the limit specified in the patent proposals ofSpaudling, Schwarz, and Wolf et al. The rolled test fixture was able tofunction on a standard roller rack, as opposed to the commerciallyavailable Rotary Cell Culture System™ from Synthecon™ Inc., and theMiniPERM™ from Vivascience Sartorius Group, which all require customequipment to roll. Thus, the scale up efficiency of the rolled gaspermeable device is much superior to other devices and approaches.

Example 4 Ability to Culture Adherent Cells in the Absence of aGas/Liquid Interface

Evaluations were conducted to assess the ability to culture adherentcells without the presence of a gas/liquid interface by allowing gasexchange to occur via gas permeable walls. A test fixture wasconstructed in a manner, as shown in FIG. 17, that eliminated thepossibility of gas transfer by way of a gas/liquid interface. Gaspermeable wall test fixture 12 consisted of a rectangular liquid tightenclosure 241, configured with one gas permeable wall 200A and fivenon-gas permeable walls 210. Gas permeable wall 200A was composedsilicone membrane, approximately 0.0045 thick, purchased from MedtronicInc. (Minneapolis). This membrane is used by Medtronic to fabricate theSi-Culture™ bag. Fluid delivery port 220 and fluid removal port 230allow inoculation and feeding. Bottom attachment scaffold 240 consistedof a section of plastic removed from a Falcon tissue culture flask inorder to provide an equivalent attachment surface as the control Falcon™T-175 tissue culture flask. The inner dimensions of enclosure 241 were 6cm deep, 10 cm wide, and 0.635 cm high. Thus, gas permeable wall 200Awas 10 cm wide and 0.635 cm high creating a surface area of 6.35 cm².Bottom attachment scaffold 240 was 10 cm wide and 6 cm deep, allowing anattachment surface of 60 cm². Gas permeable wall test fixture 12 wasfilled entirely medium during inoculation, thereby eliminating anygas/liquid interface. Thus, gas exchange could only occur by way ofdiffusion in the direction perpendicular to gas permeable wall 200A.Inoculum consisted of 60,000 live BHK cells (98% viability) suspended in38.1 ml of EMEM medium supplemented with 10% Hyclone FBS and 1%L-glutamine. Thus, the seeding density was 10,000 live cells per cm² ofavailable attachment scaffold 240 area. The surface area of gaspermeable membrane to volume of medium was 0.167 cm²/ml. The surface areof gas permeable membrane to surface area of attachment scaffold was0.106 cm²/cm². The control T-175 tissue culture flask was inoculatedwith the same cells, at equivalent seeding density and viability. Gaspermeable wall test fixture 12 and the T-175 control were placed in astandard cell culture incubator at 5% CO₂, 95% R.H., and 37° C.

Cells settled gravitationally onto bottom attachment scaffold 240 andthe control T-175 flask, and the cultures were maintained untilconfluence was reached. Both the test fixture and the control exhibiteda confluent monolayer over the entire attachment scaffold. By visualmicroscopic comparison, the cell density of both gas permeable testfixture 12 and the T-175 control flask appeared nearly identical. TheT-175 flask was trypsinized, cells were counted, and it was determinedthat cells had reached a density of approximately 190,000 cells per cm².The test fixture was subjected to Wright Giemsa staining to determinethe distribution of cells over bottom attachment scaffold 240. FIG. 20shows the distribution pattern, where “Front” is in proximity of gaspermeable wall 200, “Middle” is about midway between gas permeable wall200 and opposing non-gas permeable wall 210, and “Back” is in proximityof opposing non-gas permeable wall 210.

FIG. 20 clearly indicates that cells will grow to confluence upon ascaffold in the absence of a gas/liquid interface, mechanical mixing, orperfusion, when a wall of the device is gas permeable. Thus, gastransfer by way of walls is adequate for cell culture devices of thetypes described herein including those shown in FIG. 9A, FIG. 9B, FIG.10A, FIG. 10B, FIG. 11, and FIG. 14A through FIG. 14E to fully function.Example 4 also indicates that only one of the walls of a gas permeablecell culture device needs to be comprised of gas permeable material,thereby opening up a wide array of device design options. For example, agas permeable device could be configured in a traditional T-Flask formatby making a sidewall gas permeable. In this manner, more medium could bemade available for the culture or the device profile could be reducedsince no gas/liquid interface is needed.

Example 5 The Ability to Culture Cells on Multiple Attachment Scaffoldsin the Absence of a Gas/Liquid Interface

Evaluations were conducted to assess the ability to culture adherentcells on multiple scaffolds without the presence of a gas/liquidinterface. Gas exchange occurred via a gas permeable device wall. Gaspermeable test fixtures were constructed in a manner, as shown in FIG.18, that eliminated the possibility of gas transfer by way of agas/liquid interface. Multiple scaffold test fixture 14 consisted of arectangular liquid tight enclosure configured with one gas permeablewall 200B and five non-gas permeable walls 210A. Gas permeable wall 200Bwas composed of molded silicone material, 0.015 thick. Fluid deliveryport 220A and fluid removal port 230A allow inoculation and feeding.Attachment scaffolds 240A consisted of plastic removed from NUNC™ CellFactory cell culture devices. The inner dimensions of multiple scaffoldtest fixture 14 were 15.24 cm long, 7.62 cm wide, and 2.54 cm high.Thus, gas permeable wall 200B was 7.62 cm wide and 2.54 cm high creatinga gas permeable material surface area of 19.35 cm². Each attachmentscaffold 240A was 6.6 cm wide and 15.03 cm long, creating an attachmentsurface area of 99 cm² per attachment scaffold 240A.

In one test group of multiple scaffold test fixtures 14, four attachmentscaffolds 240A were arranged vertically, one above the other, with a5.08 mm gap between each of them, resulting in a total attachmentsurface area of 396 cm² per device. The volume of medium within thisversion of multiple scaffold test fixture 14 was 195 ml. The surfacearea of gas permeable membrane to volume of medium was 0.099 cm²/ml. Thesurface area of gas permeable membrane to total surface area ofattachment scaffolds 240A was 0.049 cm²/cm².

In another test group of multiple scaffold test fixtures 14, fiveattachment scaffolds were arranged vertically, one above the other, witha 2.54 mm gap between each of them, resulting in a total attachmentsurface area of 495 cm² per device. The volume of medium within eachmultiple scaffold test fixture was 170 ml. The surface area of gaspermeable membrane to volume of medium was 0.114 cm²/ml. The surfacearea of gas permeable membrane to total surface area of attachmentscaffolds 240A was 0.039 cm²/cm².

Multiple scaffold gas permeable test fixtures 14 were filled entirelywith medium during inoculation, thereby eliminating any gas/liquidinterface. Thus, gas exchange could only occur by way of diffusion inthe direction perpendicular to the gas permeable wall. The seedingdensity was 15,000 live BHK cells per cm² of available attachmentscaffold area. Medium consisted of Gibco GMEM supplemented with 10%Hyclone FBS and 1% Gibco Penicillin Streptomycin. The control T-175tissue culture flask was also inoculated with BHK cells, at equivalentseeding density and viability, in 30 ml of the same medium composition.Multiple scaffold gas permeable test fixtures 14 and the T-175 controlwere placed in a standard cell culture incubator at 5% CO₂, 95% R.H.,and 37° C.

Cells settled gravitationally onto each attachment scaffold 240A and thecontrol T-175 flask, and the cultures were maintained until confluencewas reached. Within four days, cultures were terminated. All attachmentscaffolds 240A were removed from multiple scaffold gas permeable testfixture 14. By visual microscopic comparison, the cell density of bothtest groups of multiple scaffold gas permeable test fixtures 14 and theT-175 control flask appeared nearly identical, at approximately 95%confluence.

This demonstrates the ability to make much more efficient use of spaceby eliminating the need to maintain a gas headspace in a culture device.Since the device only holds the medium needed to support the culture, itcan be significantly reduced in profile. The novel device is much morecompact than the traditional T-flask, NUNC™ Cell Factory, and CorningCellStack™. This results in savings in sterilization, shipping, storage,and disposal cost. Furthermore, incubator space and flow hood space areused more efficiently.

Example 6 Gas Permeable Unrolled Cell Culture Device for Adherent CellCulture Inoculated in the Vertical Position

A test fixture was constructed to evaluate the capacity of a non-rolled,gas permeable cell culture device configured with more than one scaffoldto culture cells relative to traditional flasks. FIG. 19A shows across-section of gas permeable test fixture 260. Scaffolds 120H werearranged vertically and a consistent gap was maintained between eachscaffold 120H by spacers 135B. Wall 40J was gas permeable, comprised ofsilicone purchased from Medtronic Inc. (Minneapolis), approximately0.0045 thick. Suture 270 applied force to gas permeable wall 40,squeezing it against bulkhead gasket 280 to create a liquid tight sealbetween gas permeable wall 40 and upper bulkhead 290 and lower bulkhead300. Medium access port 60B allowed fluid delivery to, and removal from,gas permeable test fixture 260. Cap 70C prevented contamination and wastightly closed during operation. FIG. 19B shows a perspective view ofscaffold 120H. It was made of tissue culture treated polystyrene, 0.040inches thick. Pipette access opening 125A, with a diameter of 0.75inches, allowed pipette access and prevented gas from becoming trappedbetween scaffolds 120H. Four vent slots 190 allowed additional area fortrapped gas to exit, ensuring that all gas/liquid interfaces wereremoved. The surface area per side of each scaffold 120H was about 86cm². The inner diameter of gas permeable test fixture 260 was 4.4 inchesand the internal height as measured from the inner surface of lowerbulkhead 300 to the inner surface of upper bulkhead 290 was 2.25 inches.Thus, the gas permeable material surface area was 561 cm². Eightscaffolds 120H were stacked vertically with spacers 135B maintaining agap of about 0.25 inch between each. The combined surface area of thetops of the eight scaffolds 120H was 695 cm². The internal volume of gaspermeable test fixture 260 was approximately 500 ml. Therefore, the gaspermeable material to medium volume ratio was 561 cm²/500 ml, or 1.12cm²/ml.

10.425×10⁶ BHK cells, suspended in 500 ml Gibco GMEM medium supplementedwith 1% Gibco Amino Acids Solution and 10% Hyclone FBS were inoculatedinto gas permeable test fixture 260P, creating a seeding density of15,000 cells per cm² of attachment surface area. A control T-175 flaskwas also seeded with 15,000 cells per cm² of attachment surface area in30 ml of the equivalent medium.

After approximately 96 hours, the cultures were terminated. Gaspermeable test fixture 260 was disassembled and each of scaffolds 120Hwas microscopically examined, indicating a confluent pattern of cellswas present on the upper surface of each of the eight scaffolds 120H.The control T-175 flask was also confluent as determined by microscopicevaluation. The T-175 flask and gas permeable test fixture 260 weretrypsinized and standard cell counting techniques were used to determinethe quantity of cells present. TABLE 6 summarizes the findings.

TABLE 6 Gas permeable cell culture device vs. T-flask Total Medium CellsViability Present Height of Medium Device (×10⁶) (%) (ml) Above Cells(cm²) Gas permeable cell 220.8 98 500 0.72 test fixture 260 ControlT-flask 26.3 95 30 0.17

TABLE 6 demonstrates that cells were able to proliferate and remainhealthy in the novel gas permeable test fixture 260, despite the absenceof a gas/liquid interface.

The volume of space occupied by each device is noteworthy. Gas permeabletest fixture 260 had a footprint of 100 cm² and a height, including theneck, of 7.6 cm. Thus, the space occupied was about 760 cm³. The T-175flask, including the neck, had a footprint approximately 23 cm long by11 cm wide, and the body was about 3.7 cm tall. Thus, the space occupiedwas about 936 cm³. Since gas permeable test fixture 260 cultured about8.4 times more cells than the T-175 flask, it would take 8.4 T-175flasks to yield an equivalent amount of cells over the same time period.TABLE 7 shows the difference in space that would be occupied if T-175flasks were used to produce the same number of cells cultured by gaspermeable test fixture 260, based on the experimental results of TABLE6.

TABLE 7 Volume of space Devices to produce Volume occupied per 221 × 10⁶cells in 3 of space Device device (cm³) days needed (cm³) One novel gas760 1 760 permeable cell culture device 260 Control T-flasks 936 8.47862

The advantage of eliminating the gas/liquid interface is clear. Over aten-fold reduction of space is obtained by gas permeable test fixture260. This leads to cost savings in sterilization, shipping, storage, useof incubator space, and waste disposal. Furthermore, the number ofdevices that need to be handled is significantly reduced, leading to adramatic labor and contamination risk reduction.

Example 7 Gas Permeable Unrolled Cell Culture Device for Adherent CellCulture Inoculated in the Vertical and Inverted Position

Using the test fixture shown in FIG. 19A, as previously defined inExample 6, an experiment was conducted to determine if cells wouldattach to both the top and bottom surfaces of the scaffolds. This couldbe accomplished by a two-step inoculation. In step one, a first inoculumwas placed into the gas permeable test fixture while oriented in thevertical position. Cells were allowed to gravitate onto, and attach tothe top surface of, the scaffolds over a 24-hour period. In step two, asecond inoculum was placed into the gas permeable test fixture. Gaspermeable test fixture was inverted to allow the cells of the secondinoculum to gravitate onto, and attach to the bottom surface of, thescaffolds.

This process was undertaken, with each inoculation consisting of enoughBHK cells to seed the exposed surfaces of the scaffolds at a density of15,000 cells per cm². Medium composition was the same as that describedin EXAMPLE 6. The time interval between the first inoculation and thesecond inoculation was twenty-four hours. The culture was terminatedseventy-two hours after the second inoculation. The device wasdisassembled and each scaffold was microscopically assessed. Cells wereuniformly distributed on both the top and bottom surfaces of eachscaffold. Subsequently, the cells were removed using trypsin and a countwas performed. The average quantity of live cells per cm² of surfacearea was 144×10⁵, with viability greater than 99%.

Cells were thus able to attach and proliferate on the top and bottom ofscaffold 120. Therefore, it is possible for the novel gas permeable cellculture device to be further reduced in size relative to conventionaldevices. For adherent cell culture, a wide variety of scaffold geometrycan exist that have cell attachment area in any plane.

Example 8 Gas Permeable Unrolled Cell Culture Device for Adherent CellCulture Inoculated in the Vertical and Inverted Position with LimitedDistance Between Scaffolds

A test was conducted to determine if inserting more scaffold area intothe device could further reduce device size. For additional spacesavings, the upper and lower surface of each scaffold was used toculture cells. The gas permeable test of Example 7 was fabricated withadditional scaffolds. The number of scaffolds and distance between thescaffolds was chosen to create a volume to surface area ratio roughlyequivalent to a traditional tissue culture flask. Recommended mediumvolume for a traditional T-175 flask varies from about 16-32 ml(Invitrogen Life Technologies). This dictates that medium reside about0.09-0.18 cm from the attachment surface. The test device of thisexample was to be inoculated in two steps, allowing cells to reside onthe upper and lower surfaces of each scaffold. Therefore, in order toget a conservative assessment of the value the gas permeable cellculture device can bring in terms of space and labor savings, 0.34 cmmedium height was allowed to reside between each of the scaffolds. Inthis manner, the medium to surface area ratio was held constant relativeto the T-175 flask. In effect, each scaffold surface had access to onehalf the medium between it, and the scaffold adjacent to it had accessto the other half. Thus, the medium available to each side of a scaffoldwas consistent with the traditional tissue culture flask height of 0.17cm per square centimeter of growth surface.

Fourteen scaffolds were inserted into the test device and evenly spacedapproximately 0.34 cm apart. A T-175 flask, with 30 ml of mediumresiding at a height of 0.17 cm acted as a control. Inoculation usingBHK cells was performed in two steps, as detailed in Example 7. Mediumcomposition was the same as that described in Example 6. Seventy-twohours after the second inoculation, the culture was terminated and thedevice was disassembled and each scaffold was microscopically assessedfor cell distribution upon the upper and lower surface. Each scaffoldexhibited a distribution pattern on the upper and lower surface that wasapproximately equivalent to that of the T-175 flask. TABLE 7 shows anexample of how increasing the surface area of the novel gas permeablecell culture device reduces the space needed to culture a given amountof cells when compared to the traditional T-175 flask. For example, whenthen novel gas permeable cell culture device contains 2432 cm² ofscaffold surface area, fourteen T-175 flasks would be needed to provideequal surface area. If 1.7 mm of medium is intended to be available foreach cm² of scaffold surface area, the volume of space occupied by thenovel gas permeable cell culture device can be determined. TABLE 8 showsthat in this case, the dramatically difference in the volume of spaceoccupied by each type of device.

TABLE 8 Gas permeable device output with increased surface area VolumeVolume of of space Available Surface Number of medium occupied area forcell devices needed per device Device attachment (cm²) needed (cm³)(cm³) One novel gas 2432 1 420 760 permeable cell culture device T-175flask 2432 14 420 12,292

It can be seen that when the gas permeable cell culture device isdesigned to have the same medium to surface area ratio as thetraditional flask, a much more efficient use of space results. Thevolume of space occupied by the gas permeable cell culture device isonly one-sixteenth of that occupied by T-175 flasks when an equivalentamount of cells are desired. This translates directly into costreductions for sterilization, shipping, storage, and disposal.

It is to be understood that the invention is not limited to the aboveembodiments, which are shown for purposes of illustration and describedabove, but is intended to include any modification or variation thereoffalling within the scope of the appended claims.

Example 9 Gas Permeable Rolled Cell Culture Device for Adherent CellCulture Inoculated in the Vertical Position

Gas permeable test fixture 260 was constructed, as shown in thecross-sectional view of FIG. 19A and further defined in Example 5, toevaluate the capability of rolling a gas permeable cell culture deviceconfigured with more than one scaffold.

With gas permeable test fixture 260 in the vertical, unrolled position,10.425×10⁶ BHK cells, suspended in 500 ml Gibco GMEM medium supplementedwith 1% Gibco Amino Acids Solution and 10% Hyclone FBS were inoculatedinto gas permeable test fixture 260, creating a seeding density of15,000 cells per cm² of attachment surface area. A control T-175 flaskwas also seeded with 15,000 cells per cm² of attachment surface area in30 ml of the equivalent medium.

After approximately 24 hours, the gas permeable test fixture was placesupon a standard roller rack at rotated at 1 RPM. Three days after thecommencement of rolling, gas permeable test fixture was disassembled andeach of the scaffolds was microscopically examined, indicating aconfluent pattern of cells was present on the upper surface of each ofthe eight scaffolds. The control T-175 flask was also confluent asdetermined by microscopic evaluation.

This demonstrates that proliferation of cells is uninhibited by rollingthe novel gas permeable cell culture device. Thus, creating a devicethat can be rolled or unrolled allows users greater options for protocoldevelopment.

GUIDE TO REFERENCE CHARACTERS IN DRAWINGS

-   10 gas permeable cell culture device-   12 gas permeable wall test fixture-   14 multiple scaffold test fixture-   15 gas permeable multiple well plate-   16 gas permeable wall multiple well plate-   20 cells-   25 buoyant shoulder-   30 lower gas permeable material-   31 non-gas permeable bottom-   40 walls-   41 gas permeable wall-   42 interior walls-   45 individual wells-   46 high surface area well-   50 medium-   55 top cover-   60 medium access port-   65 septum-   70 cap-   75 o-ring-   80 lower gas permeable material support-   90 gas compartment-   95 feet-   100 lower gas access openings-   105 tubular test fixtures-   110 projections-   115 mesh-   120 scaffolds-   125 pipette access opening-   130 inoculum-   135 spacer-   145 spring arm-   150 ramps-   160 elevation posts-   170 scaffold locator screw-   180 rotation arrow-   190 vent slots-   200 gas permeable wall-   201 top wall-   210 non-gas permeable wall-   212 tongue-   215 groove-   220 fluid delivery port-   230 fluid removal port-   240 attachment scaffold-   241 enclosure-   260 gas permeable test fixture-   270 suture-   280 bulkhead gasket-   290 upper bulkhead-   300 lower bulkhead

Those skilled in the art will recognize that numerous modifications canbe made to this disclosure without departing from the spirit on theinventions described herein. Therefore, it is not intended to limit thebreadth of the invention to the embodiments illustrated and described.Rather, the scope of the invention is to be interpreted by the appendedclaims and their equivalents. Each publication, patent, patentapplication, and reference cited herein is hereby incorporated herein byreference.

1. A method of culturing cells in a cell culture device comprised atleast in part of a gas permeable material and including at least oneaccess port and including more than one scaffold, with each scaffoldbeing positioned at a discrete location within the cell culture device,the method comprising: a) inoculating cells and a volume of liquidmedium into said cell culture device; b) orienting said cell culturedevice into an inoculation position such that said scaffolds reside atvarying elevations within said cell culture device; c) allowing cells togravitate upon said scaffolds, thereby establishing more than one celllayer within said cell culture device, said cell layers residing atvarying elevations within said cell culture device; d) making anyadjustments necessary to the volume of said liquid medium to prevent aunique gas-liquid interface from residing above each and every uniquecell layer within said cell culture device while simultaneously ensuringsaid liquid medium is in contact with said gas permeable material; ande) placing the cell culture device in a cell culture location thatincludes ambient gas at a composition suitable for cell culture andplacing the cell culture device in a position that allows said ambientgas to make contact with outside surfaces of said cell culture deviceincluding making contact with said gas permeable material; and f)maintaining said liquid medium in a static state by not mixing orperfusing said liquid medium with equipment designed to mix or perfusesaid liquid medium.
 2. The method of claim 1 wherein said access port iscovered by an access port cap.
 3. The method of claim 1 wherein saidcell culture device has two access ports.
 4. The method of claim 1wherein said cell culture location is within a cell culture incubator.5. The method of claim 1 wherein said scaffolds are adapted to becomprised of polystyrene.
 6. The method of claim 1 wherein saidscaffolds are adapted to be flat.
 7. The method of claim 1 wherein saidscaffolds are adapted to be parallel to each other.
 8. The method ofclaim 1 wherein said scaffolds are adapted to have a rectangularperimeter.
 9. The method of claim 1 wherein said scaffolds are adaptedto have a square perimeter.
 10. The method of claim 1 wherein saidscaffolds are adapted to have a circular perimeter.
 11. The method ofclaim 1 wherein each said scaffold is oriented in a horizontal plane andeach horizontal plane is at a distinct elevation when said cell culturedevice resides in said inoculation position.
 12. The method of claim 1wherein each said scaffold is oriented in a horizontal plane and eachhorizontal plane is at a distinct elevation when said cell culturedevice resides in said cell culture location.
 13. The method of claim 1wherein said cells are adherent cells and further including the step ofwaiting for a period of time until said cells adhere to said scaffoldsand then re-orienting said cell culture device such that scaffolds areoriented in a vertical plane when said cell culture device resides insaid cell culture location.
 14. The method of claim 1 wherein the volumeof liquid medium is further adjusted to provide at least 0.2 ml ofliquid medium volume for every 1 cm² of scaffold surface area upon whichsaid cells reside.
 15. The method of claim 1 wherein said cell culturedevice is further adapted so that said liquid medium resides in aportion of said cell culture device other than directly above saidscaffolds.
 16. The method of claim 1 wherein said cell culture device isfurther adapted to include at least one gas permeable material support,at least a portion of which is in contact with said gas permeablematerial.
 17. The method of claim 17 wherein said cell culture device isfurther adapted to include a gas compartment bounded at least in part bysaid gas permeable material support and said gas permeable material andthe gas within said cell culture location moves to and from said gascompartment by passive movement through at least one gas access openingin said gas permeable material support.
 18. The method of claim 1wherein the gas permeable material of said cell culture device isfurther adapted to include silicone.
 19. The method of claim 1 whereinthe cell culture device is further adapted such that the bottommostscaffold is clear.
 20. The method of claim 1 wherein said gas of saidcell culture location is at a composition of about 95% relativehumidity, about 37 degrees Celsius, and about 5% carbon dioxide.